1. Various apps generate temporary files that they need for a period. and many put them in that folder. Well behaved apps will delete them when no longer needed, but others leave them there even when no longer needed.

2. It is safe to delete them. If you try to delete one that is still in use, you will get a message telling you so and it will not let you delete it. Usually they become free to delete after the next restart of the PC.

3. Disk cleanup will delete the files in that folder that are more than a few days old, if run when logged in to the corresponding user account (in your case 'Richard').