I agree with avatar, but having said that, you've got it now, so please try & do your best by it. I kept tarantulas for many years and had no problems There are things that you should know, though :
1) Don't handle it - if it is dropped or falls, it could die.
2) They need live food. When they're small, fruit flies are ideal and as they grow, progress to maggots, then on to crickets in varying sizes. You could feed them on frozen mice (defrost first!!), but it may not eat it if it isn't moving. It is absolutely illegal to feed a tarantula (or a snake, for that matter) with live mammals.
3) If it has spun a web that looks like a little hammock, it's about to moult. It will lie on its back during the moult, and push its old skin off. Do not, under any circumstances, disturb it while it is moulting, or it will die.
4) Some tarantulas spin other webs - best to find out what species it is.
5) Look up the website for the British Tarantula Society- very helpful.
6) Get a fine aerosol bottle (like the ones you get for plants in garden centres), fill it with water and give the spider a spray with it every day. Don't overdo it, but just so's the tank is humid. Their legs work on a hydraulic system and they need this to be able to get around and to hunt.
7) Make sure it doesn't get too cold. You can buy a heat mat, which you put under the tank, but leave a bit that isn't over the mat, so's it's comfortable.
I hope this helps.