This is the Oblivion modification file (otherwise known as an ESP).
1) Load up a save game. Now save again (not quick save, and take note of which save it is). This will be the loading point every time you want to play MultiTES4.
2) Put the MultiTES4_0.2.esp file into your Oblivion's data directory, i.e D:\Games\Oblivion\Data\MultiTES4_0.2.esp.
3) Run the OblivionLauncher.exe (it's also the shortcut "Oblivion" that is put into your start menu).
4) When the launcher runs, click on the "Data Files" button. If that button is shaded out, you need to install the registry file listed above. Follow the instructions below these.
5) You will be shown a list of mods that are on your computer. "Oblivion.esm (Master File)" should be checked by default as it's the master file.
6) Check the check box next to the "MultiTES4_0.2.esp (Player File)" entry in the list. Click the "Ok" button in the bottom right of the screen.