Hey there, Popa!
The rack is secured to the Jeep by the big center bolt in the center of the wheel – as shown in the photo. The bikes are clamped into the saddels and held in place by the hand bolt. You should add your own cable lock to secure the bikes to the spare tire. If the bikes are girls bikes, they wont have a top bar, so they may be difficult to mount. We do sell a bar for that purpose.
If you're looking for specific instructions, you could always find the rack in our eStore and download the install sheet.
Hope this info helps!