We use the present simple when something is generally or always true.

We use the present simple to describe how often we do things, from never to always and everything in between. Sometimes this describes a routine or habit.  

We use this tense to talk about situations that are mostly permanent, jobs or hobbies and things that always happen. 

We can also use the present simple for short actions that are happening now. The actions are so short that they are finished almost as soon as you've said the sentence. 

We use the present simple tense for actions and events that are set by a timetable.