Use [Update record] button to add or update a record when the "file name" field is not empty. Use [Discard changes in the form] to reload information from the database to the edit form if you accidentally spoiled it. You should click [Update record] each time you want to update the record and before loading another record, otherwise the information won't be saved. When you have to update a lot of records, especially when you just begin to build your database, you can use "auto update" mode. When this checkbox is checked, the current record is automatically updated each time you leave any edit field (i.e. begin to edit other field or switch to another record in the file list). This mode is more convenient because you don't need to remember to press [Update record] all the time, but be careful with it because you cannot discard undesired changes when this mode is active. Moreover, you may spoil single records if you use Auto Update when you what to batch process other files (although checked files will be processed, the currently selected file will be also updated as soon as you leave the edit field to click [Batch Update]). So, it a word, use Auto Update only when you have a lot of manual work, disable it when you alternate manual work with batch processes.
If you no longer want Enot to find a certain image, you should drag it to the file list (or use any search method to find it in Enot), select it and and click [Delete record] button. The record will be removed from the database, but the file itself will not be deleted.