In class my friends was drawing a picture alternatively I finished my maths

A comma typically comes before "alternatively" when it is used to join two independent clauses in a sentence. For example: "You can go to the park for a walk, or alternatively, you can stay home and relax."

The recipe calls for mayonnaise, but alternatively you could use molasses.

Alternatively means in place of something else. Basically it is the choice between two or more items. Example would be Susan wanted pizza but alternatively will take a hamburger.

You could walk to the school in our neighborhood or alternatively, take a bus across town to Washington High.

She may be adopted by her foster family or alternatively face going back to an institution.