Whoops! I didn't realize you weren't familiar with canning at all.
First off, I suggest you get a copy of the Ball Blue Book and read it. That will take you through the various preserving methods. Alternatively, if there's an extension office near you, there are several free pamphlets providing the how-to's of canning. The BBB wil provide lots of good recipes as well, some of which you might find interesting as gifts.
In brief, there are two methods. For low-acid fruits and veggies you need a pressure canner. Hold that thought in abeyance until you get some time in grade. The other method, used for high-acid products and sugar-cured preserves, is a boiling water bath. Essentially, you adjust the two-piece lids on your canning jars, submerge the jars in the water (which should cover them by at least an inch), and bring the water back up to a full boil. At that point you start your timer. At the end of the time period, remove them from the kettle, set in a draft-free space, and let them cool down. The lids should seal by being pulled downward slightly by the vacuum created in the jars.
It's important, when filling the jars, that you leave head space. For jams and jellies that should be at least a quarter inch. For relishes a half inch. That's the air that will be evacuated, thus creating the vacumn.
Although it's no longer considered necessary to actually sterilize jars, I do it anyway, because there are uses for the hot water. What I do is fill the jars with water, set them in the water-filled canning kettle, and bring the whole thing to a boil. The water in one or two of the jars is poured over the lids and rings (in their own bowl). The rest goes into a plugged sink. As I fill the jars and adjust the lids, they get stood in the sink. This helps keep them warm, so there's no thermal shock when you transfer them to the kettle.
There are lots of nuances to canning and preserving, and I really urge you to consult an instructional book to learn the ropes.
You'll also need proper equipment to do this safely and correctly. That means a canning kettle (the enameled-tin kettles are the cheapest way of going). These are fairly large, and hold either 7 or 8 canning jars, and are tall enough to cover them properly with water. All the other basic equipment is available in kit form, and includes: a jar lifter; a special wide-opening funnel, a magnetic lid lifter, and a plastic "knife" used to remove air bubbles from the jars.
As a rule, jars are stored without the rings. Although many people ignore it, the recomendation is that once a jar is opened you discard the metal lid. There are optional plastic screw caps to use instead. For gift-giving I always include one for each jar in the present. You'll find that some mayo jar lids will fit wide-mouthed jars, so be sure and save them.
If your friends and relations really love you, they'll return the empty jars (and maybe the plastic caps as well). But, in general, obtaining jars is a never ending quest among home canners. And you will have to buy new lids as well---they are not recyclable in a safe manner, although the rings are.
As to not doubling the first recipe. If you do, it won't thicken and gel. Why? Just the nature of the beast. But it's usually an academic issue anyway, because most recipes produce a full canner load of jars, so there's no point to doubling anyway.
One final thought. Are you at all close to Ohio? One of our members, JamLady, not only cans professionally, she conducts lessons. If at all possible, signing up with her classes might be your smartest move.