Fake hair, aka "hair extensions", "hair falls" or "hair clips", is relatively easy to make and a lot cheaper than buying it in a store. With a little creativity, you can come up with all sorts of different looks and styles, no matter what sort of hair you have naturally. Not only that, but the fake hair styles are always temporary, so you never have to grow tired of the same ol' look!
The synthetic hair will come as one long strip in a package. Take this out and cut the strip into the desired width(s). You might want to make both wide and not-so-wide pieces, depending on where you plan on placing them on your head.
Take a snap clip and glue the hair strip onto the clip, taking care that the clip opens toward you and not away from you. For wider pieces, you will probably need to use more than one hair snap.
Make a clean part in your hair and snap the fake hair clips into your own hair. You want to get a feel for how long the pieces should be.
Now cut the hair extension to the desired length. (You might want to take it off of your head for this. If not, be careful not to cut your own hair!)
Put the hair clip back on your head as before and blend into place.
Voila! Fake hair, done cheaply and on the fly!
You should probably start with the cheaper synthetic hair and practice with this until you get the hang of making your fake hair extensions. Then, go on to the more expensive (and prettier) human hair. I recommend purchasing your supplies at an African-American or Asian beauty supply store. They will have the hair that you need, and you will also be able to purchase the clips you want. You can purchase a glue gun at any craft store or Wal-Mart for a few dollars. Before snapping the piece into place, you might want to backcomb ("tease") your hair at the place you plan on putting the extension. This will help keep it from sliding down your hair during the day. If you want funky color fake hair, you can either purchase it that way or buy it in white or a light blond and then dye it the color you want. Have fun experimenting with both color AND texture.
Be sure to let the glue dry before trying it in your hair.