Okay, I'm sick of not knowing about guitar strings, so I have some questions. I use Ernie Ball Power Slinkies. Here's what the package looks like:
Ernie Ball

11 Power Slinky
Custom Gauge 2220
Nickel Wound
Guitar Strings

Okay, so the numbers means the thickness I know. What's it measured in? Millimeters? .11mm thick?

What does the p mean besides the g string?

What does 2220 mean?

Whats the difference in different brand strings? Is it just how long they last or does it affect tone?

Thanks to all who answer.
It's measured in inches, I believe, so it's 0.011, 0.014 and so on.

The P next to the G string means that it's plated. On some heavier sets, they give you a wound G string. In Dean Markley 11-52 strings, the give you both.

don't know

Different brand is just different brand. People usually by according to personal preference. Like I use Dean Markley Blue Steel strings because they feel the best under my fingers and give me the kind of tone I want. I've used other strings, but it's just my preference.

Hope I helped.