Tip 1 of 10: Create a new library: use multiple iPhoto libraries

You can use iPhoto with more than one library. This can be handy if you want to have separate libraries for Work or Home, or split large libraries up.
Hold the Option (Alt) key while opening iPhoto to start with a window marked Which Photo Library Do you Want To Use? Click Create New to build the new library.
You can choose File > Switch to Library in iPhoto whenever you want to move to the other library.
Read:
How to set up Photos for OS X, tips for using Photos for Mac
How to use iCloud Photo sharing and iCloud Photo Library
Tips for setting up and using Photos for Mac