Click on the blue magnifying glass in the top RH corner and enter a key word for whatever you need to find eg. Word. My imac came with Word on it. The symbol is a large squidgy W on the toolbar.
To change screen saver ; click the apple, then system preferences, follow the instructions on Desktop/screensaver icon. Have you loaded any of your own photos to iPhoto, if so , it will tell you what to do.
I find macs simple, they assume ignorance and tell you in simple english what to do, and never crash.