Can i sign into another computer to use minecraft and then delete it on the other computer?

Yes!
Minecraft is 100% portable between computers. The actual game & launcher can be installed on any computer for free. It is your username that you pay for (required to play the game).
The computer will have to have an internet connection for the initial log-in.

Hell, I have Minecraft installed (and my profile logged in) on 2 computers right now.

Your single player worlds won't transfer (they are saved locally), but you can easily copy & paste the files between computers.

Multiplayer worlds should work fine.

To transfer single player worlds:
-C drive
-users
-your username
-app data (it's hidden. You need to unhide the folders in control panel)
-roaming
-.Minecraft
-saves
All of your single player saves are stored here. Merely copy & paste them to a flash drive & place them in the same spot on the other computer

I'm assuming you have a legal copy here so in this case yes it is perfectly possible. You can even keep the game on both computers. You just need to go to the minecraft website on your new computer and log in with your minecraft details (what you use to log into the game) and then you can download the game to that computer to play. You'll only be able to play logged in on one computer at a time but you can have a copy of the game on as many computers you own as you like.