The second computer

I need to know if I buy the second computer, I need to back up daedalus wallet?

Not sure what you mean. Backup is always a good idea. Putting Daedalus on a second computer is not a problem, just download and install then restore using the 12 word seed phrase you got while setting up on first computer. No need to uninstall on first, multiple instances of wallet do not interfere with each other.