Extract the file (for example C:\Program Files\otitemeditor);
Locate the Tibia folder, usually C:\Program Files\Tibia;
Copy tibia.dat and tibia.spr files to C:\Program Files\otitemeditordata;
Rename tibia.dat and tibia.spr to the version of Tibia you are using. For example, if you have version 8.60, rename tibia.dat to tibia860.dat and tibia.spr to tibia860.spr.