Recover automates some steps as described in the ext2-undeletion howto. This means it seeks all the deleted inodes on your hard drive with debugfs. When all the inodes are indexed, recover asks you some questions about the deleted file. These questions are:

Hard disk device name
Year of deletion
Month of deletion
Weekday of deletion
First/Last possible day of month
Min/Max possible file size
Min/Max possible deletion hour
Min/Max possible deletion minute
User ID of the deleted file
A text string the file included (can be ignored)

If recover found any fitting inodes, he asks to give a directory name and dumps the inodes into the directory. Finally he asks you if you want to filter the inodes again (in case you typed some wrong answers).

We hope you will never need recover, but in case, it's better to install this program anyway. Once a file is deleted, everytime something is written to disk, there's a change it will overwrite the old deleted file. You will never be able to restore it.