Help with macbook 1,1 OS

You BUY it from the Apple Online Store for 29 USD (it will work with 10.4 and 105, as it is a full Retail DVD). Then you insert the DVD and follow the instructions for an Upgrade install or to a Clean Install if you want.

To create a Clean Install (formerly known as Erase & Install) of Mac OS X 10.6 Snow Leopard (the 29 USD Upgrade DVD is a fully working retail version of Mac OS X and does not need a prior installation of Mac OS X on the Mac), follow one of the following guides:
Short version: Clean Install of OS X 10.6 Snow Leopard
Long version: Mac OS X v10.6 Snow Leopard: How to Erase and Install​