Im just really stuck what to put in one. any help will be appreciated.

Thanks In Advacne,
how did you meet?
who started the band?
former members that leave
first gigs you played
album realises and responses to them
My Gear

Squier VM p-bass(i chosed it over a fender!!!) with quarter pounder and gotoh 201!!
fender MIM P bass
epiphone SG 400
List any airplay on radio stations, as well if you've received any awards, won a poll or were a finalist in a competition, things like that. Don't list a venue you played unless it is well-known at least in your region. List bands you opened for that people will have heard of, if it's happened. Don't list previous members' bands unless they are well-known. Be sure to describe your basic genre and some of the artists who influenced you, and some you sound like. Don't laundry list a ton of groups though. More than four or five is overkill. You want people to get an idea of what the band is, and want to listen to your songs.

Don't lie about anything, but be prepared to sell yourself. No one else will. If you have any issues with grammar or anything of that nature, get someone to rewrite your bio for you who has that know how. Put out the word among friends and relatives. You may get lucky and get helped for free....or a pro writer might charge you. Might be a bit costly, but if they are a regular in an area newspaper, and they have credentials you can post that are at the bio's bottom, that can be a big boost--you're written about by a journalist with a byline the public can see, so you're serious and legit. They can also give your bio a flash and stand-out quality that you wouldn't get otherwise.
'Cause I have done it before and I will do it some more....
I do marketing and public relations full time with my business and I still have to outsource to writers for biographies. I think they are very hard to write but one tip that did help me write a few is just to look at other biographies of artists you think have great bios and kind of use that as a template. Then like said above use the who, what where, and why concept. If you can't write well then you can always outsource it to someone you know who can write well or a professional which would only run you $50-$200. If you are pushing a CD or doing medium-large marketing then a great bio is essential.
If it's for publication, or the web, try and avoid writing it like an essay/resumé. Here's an example of how not to do it:

Asparagus Now are a four piece rock band from Crosby. They formed in 2007 and have written several songs, and played in venues like the Carling Academy and Cavern Club.

Now in comparison here's the one I did for my band's site, which I reckon sounds a lot less monotonous, and hopefully gives the band a more professional image:

Burn those skinny jeans, and dig out a pair of flares! Loud, unpredictable, and smelling faintly of whisky, Asparagus Now take rock music very seriously indeed.

Why spend a fortune on a fancy stereo system, when we play all your favorite `60s and `70s tracks in glorious, hi-fidelity, surround-sound goodness? We reckon our ever-growing catalogue of classic tunes and originals makes for a great evening`s entertainment...and we hope you`ll agree.

Spending a bit of time getting the wording right makes a big difference. There's nothing wrong with just writing a list if facts and achievements like the first example, but that only works if you've actually achieved a lot beforehand....
BHowell's post should give you an accurate idea of what counts as an 'achievement', and what to leave out.