I cant tell when my space is up

Hi i am worried my space is going to be used up soon. 2 questions:

1. where can I check how much space is left?

2. what will happen when space is up?

3. where can I delete files to free up space?

Please reply me soon.

Clicking on the little human icon in the top right from nearly anywhere in the site will bring up your account usage and menu:

If you go over your limits, your forms will be disabled until you are back below the limits.  To remove files and clear up space, you would need to delete the submissions the files are attached to.  I would recommend backing up any data you need prior to doing so as deleting submissions permanently removes them from our system.