OK let's start from the beginning. What are you doing when you try and install a veh mod on your game? Are you using spark to install your mods? Like InnermostZero said we all began where you are and I'm still learning and having problems but I'm willing to try and help if I can.
Even if someone sends you a full pack you still have to install them yourself one veh at a time and thats only the vehicles you still have to install the mods for Braveheart, uniforms, radar, plate checker, K9 etc. So it's best you learn now to make things easier.