Check out the reference sheet section of the guide. The steps are all essentially the same as for ships, aside from the inability to ascend to orbit or fly, so you'll want to take a look at the "boarding a ship" and "cockpit" sections.
Like I said, look at the reference sheet I linked to. The steps for entering a vehicle cockpit are the same as the steps for entering a ship cockpit. If you're having trouble with that, please list the steps that you are following and what's happening when you try each one.