Check here for tips on selecting a scope:
Key tips for using an oscilloscope :: Radio-Electronics.Com
Part of the answer depends on what you are planning on doing with the scope, what kind of signals you are planning on working with (or see yourself working with). You can potentially buy more scope than you'll use (and pay a premium for something you don't touch - scopes aren't cheap, especially buying new). It would be like buying a Ferrari, only to use it to go to the corner store only.
Sometimes, you might find you don't need a scope at all; a lot of electronics work can be done without a scope. Other times (especially if you are doing digital work or protocol analysis), a digital logic analyzer or protocol analyzer may be called for; these are both essentially specialized o-scopes with a multitude of input channels, but they can usually only register logic levels, and how each channel relates to each other (the screens show a display similar to timing diagrams for that you see for some complex digital ICs), but they generally won't tell you that there is a "ringing" on the rising or falling edge of that signal, or what the amplitude/frequency of that ringing is. Protocol analyzers work similar to logic analyzers, but the software in them is geared toward showing not only the traces, but also what the data is that is being read; they also typically have special jacks or dongles to plug in the same type of connectors for the cable/data being analyzed (ie, RS-232 on DB-25 or DB-9, Centronics connector for parallel ports, or DB-25, USB, etc).
For most tasks, though, a simple 2 channel scope will work fine; if you can afford a 4-channel scope, go for it, and if you can afford a standalone digital scope, even better. For most hobbyist purposes, a 2-channel analog scope 60-100 MHz will work fine, and a 2-channel digital scope in the same range could be better, depending on the needs. If you can go four-channels on such a digital scope, even better (it can work as a form of logic analyzer in a pinch, if your needs are small). Anything beyond 4-channels and 100 MHz gets expensive very quickly, so keep that in mind.
Brands - if you can afford it, I would pick Tektronix or LeCroy; I have heard both good and bad things about HP scopes (interestingly, though, only good things about their power supplies).
To learn how to use one, it is best to have a scope in front of you. Just about every scope I have seen or heard about had a built in test signal; you should also try to get a small function generator to learn with (so you can use it to learn the scope, see various frequencies and waveforms, understand the graticule lines and relationships to frequencies and voltage levels, etc). In the meantime, you can start here:
Oscilloscope Tutorial Support : Tektronix
Also do a search on google for "oscilloscope tutorial" - you'll find a lot of other links to help...
Good luck!