When to use Present Tense

1) If there is no real verb
Book is red. Kitap kırmızı.
Here we have no other alternatives, so we need to use present tense. Always keep in mind that if you describe an object, the only thing you need to do is just telling the adjective. Here is some other examples for you;
Okul eski. The school is old.
Kız güzel. The girl is beatiful.
And this is same for all other words that are not real verb.
Araba nerede? Dışarıda. Where is the car? Outside.
Bu adam doktor. This man is a doctor.

2) If you make a guess or generalization

If you already studied present tense before, you probably have seen that in present tense we add -dir, -dır to the word that replaces the verb.
Bu elmadır. This is an apple.
In daily talk, nobody point at an apple and say "Bu bir elmadır" but in a book or in formal language it can be accepted. I will make it more clear with the following examples in this section.

If you make a guess or generalization or tell a fact it is okay to use,  for example;
Bence bu adam doktordur./ Bence bu adam doktor. I think this man is a doctor.

I guess = galiba
Galiba bu adam doktor. I guess this man is a doctor.
When we say "galiba" we cannot add -dir,-dır.

And about generalization;
The sky is blue. Gökyüzü mavidir. (This sentence implies the fact that the sky is blue as a normal color).
If we say just "mavi" instead, it sounds like we talk about the current time, the sky is blue at the moment, likewise;
Altın sarıdır. (The gold is yellow--all golds are yellow)
Altın sarı. The gold is yellow. (now it sounds like 'only the particular gold we talk about' is yellow)

So, if we summarize all, unless you do not tell a fact, you can skip -dir,-dır and stay safe. Perhaps, you may see it in the books, but on the street you rarely hear it.

3) If you do something continuously in a timeline, you can use present tense.
Ben her gün saat birde uyurum/uyuyorum. I sleep at 1 o'clock every day.(It is also possible to use continuous here.)
Her sabah yüzümü yıkarım/yıkıyorum, kahvaltı ederim/ediyorum ve süt içerim/içiyorum.
Every morning I wash my face, have breakfast and drink tea.

I wrote first the present and then the continuous tense. As long as we use only one of them, it is correct to use either one of them.

4) If you talk about probabilities 
Do you come to cinema tonight? Bu akşam sinemaya gelir misin?
Maybe I come. Belki gelirim.

Now the continuous ending is not interchangable with the present. So, we have to say;
Belki gelirim. Maybe I come.

5) If you ask for something
Just like the case in the sentence above;
Do you come to cinema tonight? Bu akşam sinemaya gelir misin?
Now we ask for it. But if we use the present continuous tense and say;
Bu akşam sinemaya geliyor musun? Are you coming to cinema tonight?
The speaker is just trying to learn if he/she comes or not and is not inviting or asking her to come.

Likewise, if you want to have someone to do something, again we should use the present;
Lütfen pencereyi kapatır mısın? Do you close the window please?