If you're on a PC, type %USERPROFILE%DocumentsMy GamesTerrariaWorlds into your file explorer's search bar. If your world is on Cloud Save, enter Terraria and take it off for a moment. Go back to the worlds folder, and it should be there. Click on the file once and do CRTL-C to copy it. If you want, put your world back on Cloud Save.

If this has not happened to you yet I recommend you do the following. 1. Go to your home screen and right-click, press New and create a new folder 2 Go to your documents 3. Go to Documents>My Games>Terraria>Worlds 4. Find the world (s) you do not want to get deleted, Right-click that world folder and press Copy

Go to your Terraria worlds folder (should be documents/my games/terraria/worlds) and find the world you want to give them. Upload it to somewhere like Mediafire (or since worlds aren't super big you can probably send it through skype or something if you use that) and give them the link to download it.

If you're finding a character file, copy C:Users%username%DocumentsMy GamesTerrariaPlayers into your PC's file explorer search bar. If you're looking for a world file, copy %USERPROFILE%DocumentsMy GamesTerrariaWorlds into the search bar. This should take you to your player / world file locations.