1). Open up OBMM (this is the part up above where you double-click on the desktop icon, assuming you installed it this way). Click on Oblivion Mod Manager (the second choice). Once the program opens, notice the two large 'windows': there's one on the left, and one in the center. Both are empty, except you should be seeing Oblivion.esm in the left window. Oblivion.esm is the vanilla OB game.
2). On the bottom of the program are several choices. Click Create.
3). This will take you to a new platform with several choices on it. You only need one of these: click Add Archive.
4). You might have to manually find the area of your computer where the UOP Archive was downloaded from Nexus. Let's say the Archive is in your downloads folder. Go there. Or if it's in the Modded Oblivion folder, go there. Once you do, double-click on this Archive.
5). Sometimes it seems at first as if nothing is happening, but just be patient. OBMM will sometimes unzip the archive in a split second, other times it'll take a few seconds or minutes. Smaller files unzip faster than larger ones, see? UOP takes about a minute on my comp.
6). Eventually the archive will be unzipped, if everything goes right. Sometimes it will now ask you if you want to Import info from TES Nexus? Choose Yes. The 'info' it imports can vary. Sometimes it will fill up all the blank areas, but a lot of times it doesn't. These blank areas include Name, Author, Version, the author's E-mail, and website.
7). IF it doesn't fill in these areas, this is okay. I'm an organizational freak, and I like having at least the name, author, and version filled in. I actually will go back to Nexus (or wherever the mod's from) and type this stuff in. You don't have to do this, but if you don't it might make finding the mod more difficult later on. OBMM will name a mod called 'Companion Share & Recruit' to "CSR" for instance, and in my case, I won't be able to locate it as easily.
It's up to you, though.
Note: You don't need to know this right now, but it's interesting anyways. Notice towards the bottom of the OBMM creation platform that there is a button called Plugins, and one called Data File. Plug-ins basically are mods. The two terms are interchangable. Not all archives will contain Plugins or Data Files, but you can view these areas to see if anything has been unzipped, at least. Some Archives don't contain the stuff you need (they're basically incomplete or something), but this you won't have to worry about this with UOP.
8). Click Create OMod, which is the rectangular button on the very bottom-right. If it asks if you want to add a description, you can just choose "No" if you want to skip this, or Yes if you wnat to fill this in. Personally I always skip it. I know what the mod's going to do just by its name. If you choose to fill this in, you'll be able to see your mod's description later on when you highlight it, but this is completely optional.
....OBMM will now compress and create the mod itself. This can take several seconds, or it can take several minutes. You'll be able to watch OBMM creating your mod, which is kinda neat. When it's done, it'll say "OMod created." Press Okay.
9). The OMod creation window will close, and you'll now see the original program. In the center window, you should now be seeing the Unofficial Oblivion Patch. Notice the color next to it, which should be green.
Green means the mod is inactive
Blue means the mod is active
Black means it's got some small conflicts, but the mod itself will run okay once these are taken care of.
Red means there are more serious conflicts. We can discuss this later down the road because you shouldn't be seeing red at all.
There are other colors (I think) but I don't know their meanings, nor have I encountered them.
10. Hi-light the Unofficial Patch Omod and click Activate on the bottom of the page. After a minute or so, the Omod's color should turn from green to blue (inactive to active).
11). Now look at the left window. This is showing the guts of your Modded Oblivion folder, and the UOP should now be there. Actually there should be several UOP choices, four of them. If you go to your C > Modded Oblivion folder, you'll also see that OBMM has automatically added some more stuff in the Data folder. It does all this automatically somehow, placing stuff in just the right places. Kinda neat.
12). Now go back to OBMM's left window, and hi-light each of the UOP choices. It'll tell you at the bottom left of the page what each of these choices does. There's the UOP itself, UOPS Additional Changes, the Vampire Face Fix, and Oblivion Citidel Doors. Personally I don't mind the vampire aging, and don't care about the door issue, so I only pick the first two choices, but you can choose all four if you like.
13). Go to your desktop and double-click on the OBMM icon again. Pick the fourth choice down (Oblivion Launcher). This will bring up several options, but for now we're only going to be choosing one.
14) Click on Data Files. You'll see the game itself (Oblivion.esm) along with the UOP files. If the choices you made in OBMM aren't shown here, go ahead and click on these. What you're doing is turning them "ON" basically.
15). You are done. The unofficial patch should now be working in the game.