 The two most common usages for the present simple tense are habits and routines as well as general facts and truths. Our example of routine would be I teach every Monday. We've used our subject I, our base form teach, and every Monday speaking about the routine that I have. We also have our general facts. The sun rises in the east. Here, the sun would follow under the pronoun it so we've had to conjugate our verb per our pattern and finish our sentence. We can also talk about general truths such as likes or dislikes. I like football or he likes football. Of course there are other usages but these are the two most common.