If you want to learn to sharpen a knife, grab one from the kitchen. Those make the best practice knives to learn on. Sharpening is a skill like any other and it takes time to become good. No one gets a perfect edge on their first or even second try, no matter what they say. I think there are too many people that panic because they swipe their blade on a stone a couple times and expect it to cut like a razor blade. Be realistic, pay attention to what you are doing, and be patient.
There is more than enough information in this subforum that needs some serious study. Take a moment, search through and read some of the threads. Just like in school, we learn from reading books; so you will learn from reading threads. Good Luck.
That's first-rate advice. Applicable to the whole of sharpening, regardless of which method or tool one chooses.
It's virtually impossible to actually ruin a blade, if sharpening by hand on non-powered tools. As recommended, start out on a basic kitchen knife. Before acquiring any other tools, I'd first get a good magnifier (10X or better), and examine any or all of your blades under sunlight or VERY BRIGHT artificial light, just to see close-up what their edges really look like. This is something I wish I'd done a very long time ago, would've saved me a lot of time and frustration. Fundamentally, a good cutting edge will always form a SHARP 'V' at the VERY edge (regardless of whether it's convex, v-grind, chisel, etc.). If it's rounded, or has multiple facets or sub-bevels, it's never going to be a good cutter. Good magnification will reveal just how imperfect that 'V' will be, even if it looks good to the naked eye. At sufficient magnification, a bad, UGLY edge will really jump in your face; there'll be no missing it. It seems all-too-obvious, in retrospect, that a 'V' will always be sharper than a 'U', at the edge. But, seeing it up close really hammers the point home, and will immediately clarify why a particular edge works (or doesn't).
Study up on different types of abrasives (diamond, silicon carbide, aluminum oxide, natural/arkansas, etc.), and make sure you understand WHY each works well or not-so-well (combination of grit size, type, hardness, shape of the grit particles all make a difference). Here's a good reference for starters (thanks again, to BF member zyhano):
Review - properties of abrasives described
And the most fundamental principles will always be 1.) Consistent angle control, and 2.) Consistent use of light, even pressure (let the grit do the 'grunt work').
Using one of the guided sharpeners (Edge Pro, Wicked Edge, DMT Aligner/Magna-Guide, Lansky, Gatco, etc.) can be very helpful in developing these two fundamental aspects, IF you pay close, thoughtful attention to what you're doing while you're using them. There's nothing to be gained by just mindlessly letting the 'system' do all the work. Pay close attention to WHY it works as well as it does. A guided system, for a complete beginner to sharpening, can allow you to focus on one aspect at a time, such as focusing on regulating pressure, while the guide rods keep the angle consistent. Don't have to be distracted by trying to do both at the same time.
And bottom line, if you're not PATIENT, you'll never get anywhere with learning it, no matter what else you do. Just relax, take your time, closely observe everything as you go, and enjoy the process. Make an effort to learn something new, every time you pick up the tools.
