Sailing clubs
There are sailing clubs all over the world and many (most?) cater for we mere mortals with modest pockets.
In the UK, most or all such clubs will be affiliated the the Royal Yachting Association (RYA), which provides advice, support and information for boaters of all kinds from the smallest dinghies upwards.
They are the main authority in the UK that set down the syllabus and expectations for a number of boating-related educational courses. These cover most things that my be of interest to boaters from their introductory "push the boat out" days, though courses for windsurfing, dinghy sailing, cruising, power boating, navigation, radio operation and much more. Explore their courses: https://www.rya.org.uk/training
They have a register of clubs and and training centres here: https://www.rya.org.uk/wheres-my-nearest