The best way to learn karate is to find a large glass window, get a sponge and bucket of soapy water. Take a sponge in your hand, submerge it into the soapy water, and press on the window surface. Try to cover the entire window multiple times doing circular motions with a sponge. The goal is to turn the window into a perfectly shiny and reflective surface. During the course, you will hear a lot of squeaky sounds, which means you are progressing in the right direction. When you are done with the first window, do another, and another. After dozen or so windows when your skills are honed to a decent level try doing next window while standing on just one foot. After thousands of windows on one foot try standing on a single toe. First, stand on the toe then try doing the same while standing on a single finger. After a million windows doing that you should try levitating. If you succeed, congratulations, you have become a master of karate.
The second more common way is to join a local dojo, they will instruct you and you will be assigned to a group according to your skill level. At first, you will perform a basic move (called Kihon) forward punch (oi zuki) and will do that until your arms drop off or you get good enough with it. Then you will practice other kihon. After that comes kata or form where you learn to combine those moves. There are also different styles of karate but that comes later.
Problem with second, more common approach is that you will punching air all the time and no window will get washed during the process.
