Present Simple/Present Continuous
Present Simple
You use walk(s), swim(s), etc. when it is a fact or when it happens every week/year/month, sometimes or never (when it is a habit).
You add an ‘s’ with HE/SHE/IT.
My sister (she) walks to school every day..
You walk to school every day.
Present Continuous
You use am/are/is walking, working, etc. when something is happening now, at this moment.
Look! She is walking to school!
Where is Jim? He is working.