General
Mac OS X
UsersApplications
Users can be administrators or standard users. Administrators are allowed to control much more of what happens to the Mac - installing programs etc. If you are sharing your Mac with - dare we suggest the children - it's very wise to have one administrator who has a good password, to prevent too much 'experimentation'!
This can only be done by administrator users and OS X will require you to enter your password to verify your status as an administrator. Many programs come with installers which will work automatically, but some require you to drag their icon to wherever you want to store the program - usually the Applications folder.