Do you have to drive it home or are you able to get someone to do that for you? That can make a big difference on how soon you'd actually be able to get it home since if you're on your own, you'll probably be sweating bullets if you live in a busy area/dealership is far from home.
Otherwise, standard manual driving tips, start in a parking lot, get a feel for the clutch and when it engages and how much you can play with it before it is completely engaged/stalls. This will be different between cars. Also the physical difference between gears can also get you (to stall) sometimes. When I was learning on a friends Civic, the gears were further apart so when I was test driving my speed3, I kept going into 3rd thinking I was in first a lot.
Also don't rest your foot on the clutch at any time other than changing gears. Same is true for the gear shifter. Reverse can be in different places depending on the car.
If you are uncomfortable with the car rolling back when you release your foot off the brake, try to avoid roads with any heavy inclines for a while until you're more familiar with your clutch and/or find a deserted hill and have it.
Reverse is not as bad as most people say, the main trick is to feather the clutch and it actually helped me get used to the clutch, conceptually, better than getting off in first.
Remember to lift off the gas when changing gears.
Best way though is to have that person show you how to do it. Depending on who has to drive the car home once you get a hold of it, you may want to know what it feels like to drive it and to ease any nerves you have about stalling in the middle of the street with your new car on the way home though that will mainly happen with time.
There's probably more stuff but you'll get more concise questions once you actually drive it.