OSLO is great. OSLO is horrible. In the hands of a craftsman, OSLO can do some great things. Unfortunately, in your hands, its primary product is cursing and an increase in blood pressure.
OSLO (Optics Software for Layout and Optimization) is produced by Lambda Research Corporation who generously provide a free windows executable that works with up to ten surfaces. (Mac or Linux users should run the windows executable in the WINE environment.)
The first thing is you'll need to do is to install OSLO on your computer.
You would like to do a more sophisticated design, but cannot even replicate the trivial single thin lens imaging situation that you already understand.
I assume that you know about concave & convex lenses, radius of curvature, index of refraction, and can do a simple paraxial ray trace by hand through one or two simple (thin) lenses. (If not, then the old Edmund's Brochure has a nice overview).
You've downloaded and started OSLO, but despite your l33t computer skills, you realize that there is a bit of reading of the manual required. Somewhat surprisingly, you've actually tried reading the User Guide PDF but remain baffled. Now you're at the point where your only hope is The Google. Somehow you ended up here.
Start with the single-lens ray-trace tutorial below (the others don't exist yet)