The verb sit is used to show action by the subject of a sentence. The subject will sit.
Mom will sit on the sofa.
I sit in my desk at school.
The squirrel often sits in a tree near my bedroom window.
The verb set is used when a subject places an object somewhere. The subject of the sentence sets the object.
Dad will set the money on the counter.
John will set his books on the chair.
The teacher told us to set our backpacks on the floor.
Use the verb sit when a subject itself is doing the action. Use the verb set when the subject is placing an object somewhere.
It’s your turn. Decide if you should use sit or set in this sentence blank: I ___ in the front row of the classroom. Did you figure it out? Good for you!