For home made stuff I use a word processor (Libre Office, but I'm sure Word can do all the same things)

I set up the booklet as a two cell table with fixed size 121mm x 121mm square each cell. After that, just fill in the text and graphics...

If you centre it properly and you have a duplex printer you should be able to print on both sides to make a 4 page booklet, and the same on two sheets for 8 pages if you're really ambitious.

You can also make a table-based template for tray cards, with two thin vertical cells left and right, in which you have to figure out how to do vertical text.

For properly manufactured CDs I use Scribus which is a powerful free DTP application that can produce high quality PDFs required by the printers. Any decent DTP package should be able to do the same. It's very different from a word processor and takes some getting used to but in the end more precise and better for the job.