Right click on the entry you want to use (e.g. the one named after the market on which you want to login). This will open up a context menu and allow you to copy the username or password to the clipboard.
Now all you have to do is go to the market site (e.g. registration page or login page) and paste that password there. Your clipboard will automatically clear after 10 seconds, so be quick.
To access other information stored in the entry, right click on it and then move the cursor over “Copy attribute to clipboard”.
You can also double click on an entry to bring up the editor, but be careful that you don’t accidentally overwrite any important information.