Nevertheless, my uncle showed up. So, why would he be there? And the only answer I can come up with is that he's with me a lot anyway -- and that's why he was there that night. I can't say he's with me all the time, and I'm sure there might be other explanations. But this is the one that *feels* right to me.
So, I think, if I have an uncle hanging around looking out for me, that qualifies as a guardian angel -- even if he wasn't much of an "angel" in life.

But I *still* don't understand HOW he can help me.
Well, some random thoughts. 1. Maybe he is the one that stays hanging around not moving on BECAUSE he wasnt such an angel in life, or maybe the others were better prepared to move on, and he wasnt really ready to leave the earth plane or whatever. 2. There may be a deeper karmic/past life connection that you are not aware of. More inclined to think it may be reason 1. however, but you never know.

3. how he can help you? Well spirits are capable of doing things we cant. For instance, they can see things we cant (literally, they can travel around a lot easier than we can, dont have to sleep etc. and people dont hide things from them like they would a human, they can eavesdrop and snoop easier

Not to mention, they can travel in different planes of existence easier than we can. Plus, they probably can send energy more easily than we can as well, because they ARE primarily energy.
Gina