Look into a distro that you might like, and find a "live usb" of it, often it is the installation media itself. How it works is basically it is a linux already installed on a disk image you transfer to the usb, and tell the computer to boot from it. Instructions on all this usually comes with the live usb media. Then you usually get a "try it out" or "install" option, or it just leaves you at a pre-configured desktop. Click around, install stuff, browse the web, get a feel for it.