Buy an external hard drive (you can use this for a laptop or a desktop). It plugs into a USB port and acts like a really big flash drive (memory stick) and I copy all data files onto it. It is really easy since I set up my computer with a partitioned drive. The programs are loaded onto the C:\ drive and data is saved to the D:\ drive. When I back up, I just copy the D:\ drive.
Mac systems are a little different is procedure but the premise is the same. I'm not a Mac fan but have had to deal with them in the past.