i wanna buy a Behringer XENYX 802 Mixer for live shows and recording. i do not know much about mixing boards but can you guys tell me what i should know.
What do you want to do with it exactly? What other gear are you going to use it with?

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.
was going to be used for back tracks but i came up with a better idea. so now i dont have to worry about the back tracks. sorry about this.

Mixers are ok for live shows but a small 802 isn't really that versatile...
they are also not built for recording...

If you want to record, spend money on an audio interface such as an EMU 0202 or 0404 which are both external USB2.0 interfaces. The PreSonus Inspire 1394 is another good choice and has a firewire connection to the computer.

Some places you play at will have a PA setup but if not, you need to supply that. A small kit such as one of these Phonics should do quite well.

A standard analog mixer like the 802 will not do much in terms of making your voice louder in a live setting. You need a power amp and speakers or a powered mixer and speakers to make a PA.