Английский для поступающих в вузы
Давайте рассмотрим самые простые времена в английском языке. Это - PRESENT CONTINUOUS и PRESENT SIMPLE.
(I am doing and I do)

Present Simple рассматривает настоящее как промежуток времени между прошедшим и будущим.

Present Simple употребляется, когда мы:
— говорим о вещах вообще (My son goes to school. - Мой сын учится в школе.)

— констатируем факты (All insects have 6 legs. - У всех насекомых 6 ног.)

— говорим о событиях, которые повторяются периодически или иногда (It often rains in autumn. - Осенью часто идет дождь).

Present Continuous рассматривает настоящее как действие, происходящее сейчас, в данный момент.

Present Continuous мы употребляем, если:
— говорим о событиях, которые происходят в настоящий момент (I am reading a book now. - Я сейчас читаю).

— запланировали что-то на будущее: I’m leaving tomorrow morning. – Я уезжаю завтра утром.

— недовольны кем-л. или чем-л.:
He is always telling stories. - Вечно он сочиняет.

Present Continuous (I am doing)Present Simple (I do)
The water is boiling. Can you turn it off?Water boils at 100 degrees celsius.
Listen to those people. What language are they speaking?Excuse me, do you speak English?
Let's go out. It isn't raining now.It doesn't rain very much in summer.
I'm going to bed now. Goodnight!I always go to bed before midnight.

Внимание! Следующие глаголы не употребляются в Continuous: be, have, hear, know, like, love, see, smell, think, want... Полный список
This is how a native speaker explains the difference between the Present Continuous tense ("I am doing"), and the Present Simple tense ("I do").

Which tense you use depends on how you see the state or action. If you use the Present Simple ("I do"), you think something is permanent. This means we often use the Present Simple to talk about general and scientific facts, our routines or habits, to give definitions and to describe things.

The Present Continuous ("I am doing") means the action is happening now (or around now), is unfinished, or temporary. We use it to talk about trends and changes, or about situations happening now that are different from normal.

"I live in London." (This is my home.)

"I am living with my parents." (A temporary situation until I buy my own house.)

"Hot air rises." (A scientific fact.)

"House prices are rising." (A trend happening now.)

"I drive to work every day." (My routine or habit.)

"I am walking to work this week." (My car is being repaired.)

"At work I write letters to customers." (My job routine.)

"I'm writing a difficult letter." (This is what I am doing right now and I haven't finished yet.)

So the most important rule is that you use the Present Simple ("I do") for permanent states and the Present Continuous ("I am doing") for changes and trends.