When I bought my '08 Dodge, it already had Firestone Ride-Rite air bags installed. If you want to spend the money for on on-board compressor, you can adjust them from the drivers seat. It'll cost you more than the air bags. Mine don't have that as I don't need them often enough to justify the cost. There's an air valve on the side of the frame above each rear tire that's filled with an air hose.
The instructions say to keep at least 5lb in them at all times. They'll take up to 100lb of air which will hold more weight than your axle will (5000lb max). You still can't exceed the weight rating of the truck as the hubs, bearings, etc. can't take it. I find that about 60lb will give me all I need, even with a full load of hay. To fill them, load the truck 1st, then add air to bring them up to the correct ride height. The instructions show you how to measure them to get the right height. After doing it once or twice, it's easy to eyeball the bags to know how much air to add. It only takes a couple min to fill them but to do it at home you have to have some kind of compressor. Any shop compressor will fill them in seconds. A 12v inflator will do it but it'll be much slower. I tried doing mine once with one of those jump start units with a built in inflator. It took a very long time as they slow way down when you get much over 40 lb.
I also have a 120v tankless compressor that puts out up to 125lb. It works as fast as a tank type and I don't have to wait until the tank fills. I just switch it on and instantly have full pressure. It takes me longer to get out an extension cord than it does to fill the bags. It's very handy for small jobs like this. I got mine from my dad when he died but you can buy one for around $50.
Here's the website for the ones I have. You can go to the one that fits your truck and pull up the instructions to see what you're up against.
RIDE-RITE 
