A systems tool kit is like a tool box for your computer! It's a set of tools that can help you make sure your computer can do all the things you need it to. Just like if you have a tool box, you have a hammer and a screwdriver, a systems tool kit has tools to help your computer run smoothly, like a disk cleaner to get rid of things that aren't necessary, or a file backup tool so you don't ever lose important things you saved to your computer.