How to stop Start-Up Apps?

Is there anyway I can choose what certain programs should run when the computer boots up? There is a program that appears at the top by the clock every start up and I dont want it there so I just close it. There is also another program that I would wish to not make it start at startup.

Thanks.

Go to System Preferences > Users > Choose your account > Login items

There you can set which Apps will be launched at startup, and which ones will be hidden after launch.

Ah. thank you!