To use SystemRescueCD, just boot it up. It will ask you for a keymap preference; if you ignore it and wait it will select a US keyboard by default and finish booting. If you are using the bootable USB image, be sure to test it a lot on different systems. Any PC made in this century claims to support booting from USB devices, but this isn't always reliable. Still, it's the ultimate in cool to whip out your Swiss Army Knife with the built-in USB stick and boot computers with it. SystemRescueCD uses around 380 megabytes, so these days you won't have any trouble finding a USB device with enough capacity.
SystemRescueCD doesn't automatically set up networking, so run the net-setup command after it boots up to configure networking. startx gives you WindowMaker. If you have any problems starting SystemRescueCD, reboot and hit the F2-F5 keys to see a lot of helpful information on boot options.