Over 3-5 days you will learn the skills to competently crew a yacht. You will be able to deal with a fire below, help with a man overboard situation, as well as be a reliable crew member in most situations at sea. Though you may be a complete novice when you begin, you will be considered a useful member of crew for a yacht racing around the buoys or on a coastal passage.
You will not be able to skipper a yacht, though people with the Competent Crew are considered effective and useful members of crews on all but the most racing oriented boats. This opens the door to a lot of fun cruising and day racing.
Competent Crew is a practical course though you will be introduced to things like navigation and meteorology that will be developed as you progress through the RYA course structure.
You can take it at any sailing school in the world that offers RYA accredited courses.
In short, yes. There are RYA qualified instructors around the globe.
You can be a complete novice though the course will be shorter if you have done the RYA Start Yachting course as you will have some idea what to do when asked to “clean the heads” – you won’t be mopping the skipper’s brow…
5 days, which can be done during the week or over a series of weekends
This is a fairly serious introduction to sailing. You will learn ropework, parts of the boat, sail handling, helmsmanship, manners and customs of sailing, safety equipment, what to do in emergencies such as a fire or someone falling overboard, how to help yourself or someone else who is seasick, the rules of the road, and the duties involved in sailing a boat.
You can progress through the RYA course structure. The next course you will do is the RYA Day Skipper.
Look elsewhere on this website to get an idea of when and where is convenient to do a course, but also look at this section of the RYA website to see what exactly the course involves.
Other resources can be found on this Wikipedia page.