The present is now and the simple present tense is used to talk about actions that happen now. If you do something every day, or sometimes, or usually, or every Saturday, you use the simple present tense.
How does your maths teacher keep fit during the week? He walks to school every day. He plays badminton on Monday and he goes swimming on Tuesday. On Wednesday he cycles in the park and usually on Thursday he meets friends at the gym. On Friday he coaches a junior football team.
At the weekend, he is usually lazy. He relaxes on Saturday and on Sunday he stays in bed. All these are repeated actions, done more than once in the present, so they need the simple present tense.
We also use the simple present for facts that we know are true. Koalas live in Australia. I like koalas. Koalas eat eucalyptus leaves. Koalas sleep all the time. Koalas hardly drink anything.
The simple present is very easy to use because it is only one word. It is a very important tense and is used a lot in conversation because we like to talk about what we do all the time or what other people do.
We also like to give facts when we talk. I hate our new maths teacher. She is so strict. She shouts all the time and picks on me. She gives us so much difficult homework ... and she wears awful clothes. I loathe her!