Step 7: If...
If this is your cat's first cardboard scratcher, put it near where she likes to sleep, and occasionally place the cat on the scratcher just as she's waking up. Cats like to stretch and scratch right at waking, and it doesn't take them long to learn that the cardboard "tree bark" is the ideal place to do that. Our cat naps right on the thing to save time commuting. We've found scooping the cat up out of her nap, and pouring her onto the scratcher (front feet first) seems to give her a pre-stretch that leads to scratching every time.
If the cat really, truly does not seem to know what to do with it, scratch on it with your own fingernails while he watches. The motion and sound are both useful because cats learn easily by imitating us. You can also gently rub his front paws on it, to further provide the idea. Try not to freak him out, or he'll never go near the thing again.
Most adult cats won't actually climb the thing, since it is only about as long as their body, but it's better if it's not attached to something unstable or very light. For instance, a mop handle is a poor choice. You can also just lean it up against things (walls, the end of the couch where she used to scratch...). Our cat learned the exact technique for getting better scratch without knocking the thing down.
If the top surface of the scratcher gets all used up and ratty looking, just cut the tape, flip the accordion over, and re-tape it.
If your cat dispenses bodily substances onto it or something spills on it, or it gets rained on, remember that cardboard is absorbent, not washable, and free. Cats who get a lot of hairballs like to stand on the scratcher to vomit, because it gives good traction, but usually they puke over the side.
If your cat is a sheep, like our cat, you may want to get the shed hairs off it with the cat's brush, or even vacuum it occasionally. This will be somewhat traumatic to the cat if he is on it at the time.