Like many areas of the Spanish language, it is essential that we have a basic understanding of the present subjunctive.  Usually any time there is a sentence that has an element of uncertainty, desire, hope etc., verbs are changed to reflect this.  We need to be familiar with at least the basics of the present subjunctive because if we fail to conjugate a verb or verbs when it is called for, it will sound way off.   Knowing when to speak in the subjunctive is the challenging part.  Sometimes a sentence is subjunctive and sometimes it is not and this can be difficult to explain why.   However,  there are many obvious situations for when a sentence is subjunctive.  If you can at least recognize these, no doubt your Spanish will improve.  In general, a subjunctive sentence always has some unknown, some uncertainty, something uncontrollable and or something that has not happened.  We will look at this in more detail and identify some of the most straightforward and obvious situations that will ‘trigger’ a subjunctive sentence.  But first let’s look at how regular verbs are conjugated in the present subjunctive.  

First, take the “yo” (me, I) form of the verb in the present tense. For example:

Ver- To see- Veo.
Salir- To go out- Salgo.
Tener- To have- Tengo.
Hacer- To make or do- Hago.
Comer- To eat- Como
Conocer- to know (someone)- Conozco
Hablar- to talk – Hablo
Esperar- to wait or hope - Espero

Then drop the “o”: Ve, Salg, Teng, Hag, Com, Conozc, Habl, Esper.  

And then, for “ar” verbs, in place of the “o”, add:

e, -me, you, he, she, it. (yo, usted, él, ella),
es –you (informal, tú),
en –they (ellos, ellas).
emos –us (nosotros).

And for “er” and “ir” verbs in place of the “o”, add “a” and the respective endings.

For the example verbs above we have their (present) subjunctive forms:

Vea, Veas, Vean Veamos.
Salga, Salgas, Salgan, Salgamos.
Tenga, Tengas, Tengan, Tengamos.
Haga, Hagas, Hagan, Hagamos.
Coma, Comas, Coman, Comamos.
Conozca, Conozcas, Conozcan, Conozcamos. (Remember a “Z” is always pronounced like an “S”).
Hable, Hables, Hablen, Hablemos
Espere, Esperes, Esperen, Esperemos.

There are several verbs that do not fit this pattern, but not that many.  You have to memorize their conjugation.  The more commonly used ones are conjugated like this:

Estar.- To be, condition or location- esté (me,you,he,she,it) estés, estén, estémos.
Ser- To be, permanent situation- sea, seas, sean, seamos.
Dar- To give.- dé, dés, dén, démos.
Haber- To have done something- haya, hayas, hayan, hayamos.
Ir- To go- vaya, vayas, vayan, vayamos.
Saber- To know- sepa, sepas, sepan, sepamos.  
Now let’s look at some basic subjunctive sentences.  Probably the most classic example of a present subjunctive ‘trigger’ is when a person wants, hopes or desires something to happen.  A sentence like this is usually divided by “que” which means “that” or “to”.   Ok, ready?

I hope (that) you have a nice day.  – Espero que tenga(s) un buen día.  
We hope (that) it does not rain. – Esperamos que no llueva.
She hopes (that) they arrive on time. – Espera que lleguen al tiempo.  
I want you (to) mow the yard now! – ¡Quiero que corte el césped ahoro mismo!
We want you (to) change the light bulb when you can. – Quieremos que cambie la bombía cuando pueda.
We hope you know the answer.- Esperamos que sepa la respuesta.
They want you to give us the money. – Quieran que nos dé el dinero.
I don’t want you to be like that. – No quiero que seas así.  

The first part starts out normally. “Hoping that”, and “I want you to”.  The second part contains the subjunctive verb.  Do you see why these are subjunctive sentences?  If you hope for something to happen, it may not happen.  If you want someone to do something, they may not do it.  All outcomes are uncontrollable and have not happened yet.   

Here is another simple recognizable situation on when a sentence is subjunctive.  Usually when a sentence starts out with “maybe” or  “perhaps”, it will subjunctive.  Right off there is uncertainty.  Use “tal vez” or “quizás” to mean perhaps or maybe.  Just to note, sometimes a sentence like this does not have to be subjunctive.  It can go either way.  But if you always make these subjunctive you will never be wrong.  Look at these:

Perhaps you know him. – ¿Quizás lo conozca(s)?
Maybe they will improve the golf course. – Tal vez mejoren la concha de golf.  
Perhaps we can study Spanish tomorrow? – ¿Quizás podamos estudiar español mañana?
Maybe they will repair the roads in Coronado? –¿Tal vez arreglen las calles por Coronado?
Perhaps they will go to Panamá tomorrow. – Quizàs vayan a Panamá mañana.  

Many times, (but not always), the Spanish word “cuando”, which means ‘when’, will set in the present subjunctive in motion.  Look at these two sentences:

I will start to cook when our guest arrive. – Empezaré a cocinar cuando nuestros invitados lleguen.  
When I am in Panamá I always stay in Coronado. – Cuando estoy en Panamá, siempre me quedo en Coronado.

The first sentence is subjunctive, as the guests have not arrived and may not arrive.  The second sentence is not subjunctive because it is implied that I have been to Panama before.  Here are a few more examples of when ‘cuando’ makes a sentence subjunctive:

(1.) Come when you want. – Venga cuando quiera.
(2,) Do it when you can. – Hagalo cuando pueda.
(3.) Close the door when you leave.  Cierre la puerta cuando se vaya.

The three sentences above actually have two verbs conjugated in the subjunctive.  This is because there are two elements triggering the subjunctive.  In (1.) is the desire for someone to come, (2.) the desire for someone to do it, and (3.) the desire for the door to be closed.  The second part is the uncertainty. (1.) They may not want to come. (2.) He or she may not be able to do it. (3.) He or she may not leave.  

Other very recognizable situations in the subjunctive are:

Doubt:  I doubt that they are coming. – Dudo que vengan.
An action that is not completed: - I will believe it when I see it. – Lo creeré cuando lo vea.  
A non personal opinion:  It’s better if you can speak Spanish in Coronado.  – Es mejor si pueda(s) hablar español por Coronado.  
An ‘even if’ statement:  Even if you know the answer, you will not tell me. – Aunque sepa la respuesta, no me dirá.  

There are other situations that call for the subjunctive, some not so easy to identify.  When you hear a verb in a sentence that is subjunctive, see if you can understand why.  If you can’t, don’t worry, just accept it.  Try to recognize the obvious situations, like the examples above.  

And (always) try to keep the learning of Spanish fun.  If you can have fun with the subjunctive, it is a good sign you have already learned a lot of Spanish and want to learn more.  You are no longer a beginner if you can speak with just the basics of the present subjunctive.  

altHope this helps!