How can I transfer mp3 files from my PC to my Ipod Touch 4?

I have an Ipod Touch 4 that was given to me. I use it almost exclusively to listen to audio books downloaded from various libraries. Once upon a time long ago I did manage to download some music (mp3 files) to the Ipod but I have no idea how. Now I would like to transfer some additional mp3 files to the Ipod but I have no idea how to do so and I have not been able to find any instructions that make sense using Google. I should also mention that I find ITunes to be the most confusing non-discoverable software I have every encountered. The instructions for dummies won't do. When it comes to ITunes I need the instructions for someone who can just barely find the on/off switch with both hands in daylight. Thanks for any help.

P.S. I developed business application software for 40 years so I am PC literate, just not ITunes and Ipod literate.<g>