Revising means to change things in the text!
When you are done with the first draft you should always revise.
All you need to do is to make corrections in your story, report, assignment, etc.
For instance, if you wrote this: Me and my sister went to the park.
You should change it to: My sister and I went to the park.
Also, there might be things that you dont want, so this is the time to delete them.
As you read through the text make sure youre saying what you want to say.
If you forgot something, now is the time to add things.
You might want to reorganize things.
Maybe you put in a sentence that doesn't match or doesn't fit with the other sentences.
Revising is only a step before editing where you make the big changes!