The present simple (sometimes called simple present or present indefinite) is used when something is happening now or when it happens regularly.
We make the present simple by adding 'es' or 's' to the root verb:
walk - walks
graduate - graduates
You can use it to talk about your routines: "She eat breakfast at 8"; or schedules: "The bus arrives at 8.30"; or when something is always true, such as, "It gets bright at 9 am". When we tell jokes or we comment on sports that are happening 'now' (at the time we are speaking): 'He kicks the ball'; "An Englishman, Irishman and Scotsman walk into a bar...".
When we are explaining how we feel or what we are sensing in the current moment we use the Present Simple tense, too. So, you can use the present simple to say, "I feel sick", or "I hear music". The Present Simple can even be used to talk about things that are expected to happen in the future, or future plans, such as "He starts school in September"; or "She competes in the competition in March".
With so many uses, it's no wonder that it makes up almost half of our speech and written communication!