singlespeed
theres not much to do at all really just remove all the stuff you dont want, fit a cheap singlespeed converter and make sure your chain is running straight when you look from the rear single cog back up to the big fornt one.
adjustment can be made by washers either way on your front and rear cogs and wether you fit your front cog outside or inside the spider to get it as near as poss to straight line
gearing is a bit trail and error till you get used to the limitations of not being able to get up huge hills without regurgitating breakfast and not being able to keep up with the pedals down big ones " if you stay with the ratcheting rear end that is"
I personally favour being able to get up the hills and loosing a little speed downhill and run 36-13 but that's not a common gearing and my bike is a 29er
the chain tension is sorted by fitting your gears as you want them and seeing how slack the chain is if it is only a little slack a half link chain will sort it if it's really slack or super tight you may need to bolt on a chain tensioner where your mech used to go to stop it flapping around
any questions on any aspect and you can always give me shout.
Darren