This method of canning is by far the simplest, and can be done in a turkey roaster.  It is only recommended for acidic foods because the internal heat doesn't reach the temperature necessary to kill all possible bacteria (my grandmother used this method for everything, and never had problems - I'm not recommending it, just passing on the thought that if I had to decide between losing my crop or using a boiling water bath, I know which one I'd choose).

Foods which can be safely processed using a boiling water bath:  tomatoes, pickles or anything preserved in vinegar (hot peppers, for example), jams and jellies, apples or applesauce (See Canning - Recipes).

Equipment:  Canning jars and lids (I've always had more jars seal when using Ball); large container with lid for the boiling water bath (any large container can be used, but either a turkey roaster or a regular pressure cooker are ideal), a pan for boiling the lids and another one for blanching the tomatoes, a tea kettle(s), tongs, funnel (I make one for this - cut up an old vinegar bottle or something - the opening should ideally be wide enough to just fit in the top of the canning jar), and a large bowl of cool water.

Getting Started:

1)  Boil water - lots of it.  Put your turkey roaster (about two thirds full) or canner onto the heat (when I use a turkey roaster, I use two burners), cover it, and bring it to a boil (top off as necessary).

Put the lids for your first batch into a saucepan full of water and bring it to a boil.  I just let it keep boiling until I'm ready for them.

Boil enough water in a tea kettle or other container to fill the canning jars for your first batch to the very top.  Fill the jars and let them stand until you're ready to fill them.

2)  Put the fruit or vegetables that you are canning into the jars (See Canning - Recipes).  Fill them to about 1/4 inch from the top, and very carefully wipe the rim of the jar - if you leave traces of food on the lip of the jar, it will prevent proper sealing.

3)  Remove the lids from the boiling water (using tongs) one at a time.  The lids are in two pieces - put the flat top on first, then screw on the outside of the lid (firmly, but not excessively tight). 

4)  Put the jars into the boiling water.  If you are using a canner, it should have a basket - when I use a turkey roaster, I just put them in.  Cover and boil for the designated time (see Canning - Recipes) for times.

5)  Remove the jars and set aside.  As they cool, you will hear a popping noise, and the lid will be depressed.  Once they have cooled completely, you can remove the outer lid and reuse it.

6)  Generally speaking, if a jar doesn't seal, you should just stick it in the refrigerator and use it, though I have occasionally repacked and canned things a second time.