When you have a cold you should stay home until the cold virus has gone away which is around 7 to 10 days.
If you have a cold you really should stay home for the full 7 to 10 days just to avoid getting other people sick and also you won't feel good enough to do any work if you're going to work or even at school you'll be feeling awful.
However if you do start to feel better within 3 to 4 days then you might be able to return to school or work but continue to stay hydrated, take some over the counter cold medicine etc to help you feel better.
You still may be contagious with your cold virus for the full 10 days but usually you'll be much better within a few days and can return to work or school.
But I've always just stayed home the full 7 days until I felt better.