First off, moleskin can be bought at most drug stores, big box retailers (Wal-Mart, Target, Meijers if you're lucky enough to have one, etc) and many grocery stores. Look near the bandaids or foot care products. Dr. Scholls makes some, so look for the yellow package. Costs a few dollars for a package.
As for how to use it, there are a couple of different ways.
1. If you regularly get blisters in certain spots while wearing certain shoes (or while wearing any shoes). Put moleskin on that spot before you leave in the morning (although, if you're regularly getting blisters, you've probably got callouses there already. But, ya know. Some people juggle geese.)
2. If, while you're on your feet, you start to feel a hot spot or somewhere where your shoe is rubbing, you put mole skin on that spot. Sometimes this is hard to notice before a blister actually develops. But, if you take your shoes off and notice a spot that is noticably redder than the surrounding area, it's a pretty good bet that area was being rubbed and, if you continue to wear the same shoes, you will probably develop a blister there, so not a bad idea to go ahead and put some moleskin on.
3. If you discover you've already got a blister, you can still use moleskin. Although instead of applying a piece directly to a blister, it takes a bit more work. You need to cut a piece of moleskin considerably larger than the blister. Then, cut out the center of the piece such that the hole you cut is the size of the blister. So, you end up with a donut shape of moleskin where the blister fits in the hole. Basically, you're building up the area around the blister so that your shoe rubs on the moleskin and not on the blister. Put the moleskin on and you should be good to go.
4. Alternatively, you can put the moleskin directly on the shoe, where it rubs you. Sometimes this works, sometimes it doesn't. Depends on the shoe, how well the moleskin adheres, how the shoe is rubbing, etc. There's lots of variables.
There are some alternatives to moleskin.
For smallish blisters on parts of your feet that aren't flexing a lot, you can often use foam or sport bandaids (I recommend the Band-Aid brand. They seem to be the best and the best adhesive). If you've already got a blister, put the band-aid pad on the blister. If you've got a hot spot, cut the adhesive part off the band-aid and put that on the hot spot.
Duct tape can also work wonders. Use it before you get blisters, the same way you would use moleskin. Usually works best if it's applied both to your foot and to the shoe. The duct tape on duct tape helps to reduce the friction and direct rubbing on your skin and thus, helps to reduce the possibility of geting a blister.
If you do get a blister, there's some basic care tips I've found work for me.
(Standard disclaimer. I'm an engineer, not a doctor. I do this to my own feet, but try this at your own risk. You have been warned.)
First, if you're going to take a bath or shower soon, wait until after you get out of the shower to do this. Skin under blisters is very sensitive and water that just feels nice a warm to regular skin will really hurt blistered skin.
If your blister is small and not filled with liquid or anything, bandage it to keep it from rubbing and getting worse and leave it alone.
If there is liquid and/or blood in the blister, you need to drain the liquid out. To do this, sterilize a small pair of scissors, pocket knife, pin or needle (use a match or rubbing alcohol) and the blister and area around the blister (rubbing alcohol's the way to go here). Then, at the edge of the blister, carefully puncture the blister. Make as small a hole as possible and squeeze the fluid out. If the blister is larger, you may need to make another hole at another location around the blister. (Note, this may hurt and may be icky. You have been warned.) If the blister is small and/or not too deep, bandage it and you're good to go.
If the blister is large and/or deeper (the redder the skin under the blister is, the deeper it is and the more it hurts), I generally make a little bigger hole and squish some neosporin with pain killer (cause these big blisters hurt like nothing else) in and massage it around. It's important to get the neosporin inside the blister. Outside it's not going to do anything. Then bandage it with bandaids such that the whole blistered area is covered.
Check the blisters at least once a day. If the holes have closed up and the blister has refilled with liquid, make another hole (or find the first one) and repeat the procedure. If you've got a larger blister and the skin continued to be red and painful, repeat the neosporin step.
Watch for infections. If the blister doesn't heal up in a day or so or starts to ooze puss (rather than just clear liquid or maybe a little bit of blood), then it's time to get them looked at by someone.
