They are pretty self-explanatory.
"Delete" deletes something.
"Format" refers to several different ways of formatting: italics, font size, font style, colour, bold, centering, etc. Are you talking about text? A page? Forum-specific capabilities? ...
Delete : -
Deleting is a process in which a user deletes data by selecting it. Deletion of data from a computer can be done temporarily or permanently. If a user uses the Delete button from the keyboard to erase some file, it moves to a temporary folder known as the ‘Recycle Bin’.
Formatting is a process where the entire drive is formatted i.e. the entire data in a particular drive gets erased permanently. It is usually done to empty the drive when the data present in it is not required.