Need help stopping applications from launching at startup on my macintosh computer?

i have an imac - whenever i restart the computer a game called nansaur and the system profiler application launch. i know that there is probably a "startup" folder somewhere on the OS that i cannot seem to locate (i'm very windows savvy but am about a year into my mac apprenticeship!). would love it if someone could help me to remove these applications so that they do not launch at startup!