I bought a computer and it has no hard drive.I have a hard drive from another computer so what do i need to do when i put it in

Is it a SATA drive or IDE/ATA? Do you know how to simply install it and connect it to power and data cables?

After the physical install what do you want to do?

Install a new operating system?

You cannot just use the old hard drive as it was if that was your intention. You would need to wipe it and install a new operating system.

How do i tell if it is a sata or ide/ata.When i got the camputer it had no hard drive so what i want to do i take the the one out of my old computer and put it in and ur saying that i need to whipe it out before i put it in.

You can wipe it afterwards as well.

Point being that after you install it you will need to clean load an operating system.

If you choose a Windows system you will need a distinct product key not used on any other computer.

Of course you could also use ubuntu for free.

Ubuntu Home Page | Ubuntu

Yeh, the reason you have to reinstall (besides legal stuff), is because the operating system is confugured to the motherboard, processor etc in your old machine..
Ubuntu is a very good choice, or you could get Xandros, it isnt free, but it's pretty cheap and is very good for making a transistion from windows to linux