Select the repos you want, make sure you are connected to the internet, then say "yes" when asked to reload the repositories. It'll take a couple of minutes to download the list of packages available - there are quite a lot already. You would normally have packages, patches and extra selected. You might also want to have testing selected as many packages are in testing at the moment for VL7. I'm not sure that adding slackware to the reps is a good idea, maybe others will comment on this.