如何使用NSUserdefaults保存设置

I am making a tip calculator and the requirement is to have a settings page to go along with the calculator. In the calculator there are three options implemented by a segmented control when each is selected, the value of the tip and the value of the total change. In my settings tab I would like to be able to have the user save their default tip percentage. I know I need to use NSUserdefaults, however I do not know how to do this using two different pages (or one page for that matter). If what I want to achieve is unclear, please let me know I tried my best explaining it thoroughly. I am making a tip calculator and the requiremen