Theory:

The Present Simple

The present simple is only used for something that is true now, something that is always true, or is fixed in the future, or happens regularly.
It cannot be used for something that happened in the past, or is happening right now.

For example,
I speak French. (true now)
The sun rises in the east. (always true)
The train leaves in 2 hours. (fixed in the future)

Words like sometimes, often, usually, always, and never, (adverbs of frequency), are normally used for things that happen regularly.
For example, I usually play tennis on Sundays, but I never work on Saturdays.

It is formed by using the base form of the verb, for example, I PLAY tennis,
But in the third person, (she/he/it), an 's' is added, for example, he playS tennis.

The contraction DON'T is used for DO NOT, and DOESN'T for DOES NOT.

In the negative and interrogative forms, it uses the auxilliary 'DO', for example, I DO not play tennis, or DO you play tennis?
In the third person, (she/he/it), the auxilliary used is 'DOES, for example, He DOES not play tennis, or DOES he play tennis?

Common Mistakes:
1 I work yesterday. (PRESENT SIMPLE not valid for the past.)
2 I wait for you at the moment.(PRESENT SIMPLE not valid for right now.)
3 I wait for you for 10 minutes. (PRESENT SIMPLE not valid for duration in the past.)
4 What are you doing? I eat. (PRESENT SIMPLE not valid for right now.)
5 He play tennis every week. (PRESENT SIMPLE needs an S in the third person.)
6 She do not like meat. (PRESENT SIMPLE needs the auxilliary DOES in the third person.)
7 Do you wants more tea? (PRESENT SIMPLE does not accept S unless in the third person.)