Information is here: http://www.tesnexus.com/downloads/file.php?id=13841 .

My question is, well, what does it actually do? (started playing Oblivion just a couple of days ago, so I'm confused)

Just as it says in the description:

This mod increases the hardcoded ATTRIBUTES and SKILLS, level caps from 100 to 200 for all actors in game including the player.
The following hardcoded formulas have been modified to make use of attributes and skills up to level 200:
- WEAPON DAMAGE
- HAND TO HAND DAMAGE
- MAGICKA COST

So the Blade, Blunt, Hand to Hand, Athletics, Acrobatics, Marksman Illusion, Conjuration,Mysticism, Alteration, Destruction, Restoration benefit from the uncapped values.

Say you have a Blade skill of 40. In time, you can get this to 100, but it won't go any higher in the vanilla game. With Elys Uncapper, it can climb as high as 200. Whether this actually has any effect or not on your particular style of gameplay depends on the individual equations used for each of the skills.

Having just started playing, it won't affect you yet.
But there is an upper limit to how far your (and NPCs) skills and attributes can level up to. This mod shifts that limit to a much higher one. Meaning that you can keep on increasing your skills for longer, rather than reaching you limit and no longer really gaining anything from practising your skills (e.g. fighting with your sword will no longer make you any better at doing that, once the limit is reached.)

Basically it allows you (and your opponents) to continue getting better at what you do, for longer.

The primary reason for the mod is that many people tend to get bored playing a character once it has reached its 'growth' limits.

Elys isn't developing this one any more. However Jrousch (spelling?) IS working on one. Have a look http://www.gamesas.com/index.php?/topic/1157256-relz-av-uncapper/.

Thanks very much, kindred spirits. Vargr, your explanation is exactly what I was looking for. Thanks fable2 and Heyyou as well :foodndrink: