how to music on ipod???

I have an old ipod shuffle, and I want to put my itunes music onto this.

I pay a monthly fee to listen to itunes, and I think I cant put music on my ipod because I have not purchased it.

Anyway, I don't mind paying for the music again, I just want to put music on my little ipod so that I can go running with it.

I'm not really very techy so I don't really understand this, I wish there was some sort of button I could press so that I could repurchase all the music in a playlist and then copy it onto my little ipod shuffle.

Thanks in advance for your help people.....

Simone