While the brand of your clubs is entirely up to you, every golfer should have a driver, a set of irons, wedges, and a putter. These will be used on almost every hole, so make sure you get a set that is comfortable for you and that you like them.
No! While some golfers are members of private courses, there are plenty of public golf courses open around the world that require no membership and only a cost for a tee time. Prices will vary by course, but you definitely do not need to become a member somewhere just to play golf.
While a few courses do not enforce a dress code, it is common for all golfers to follow some sort of dress code. It is common for male golfers to wear a polo/collared shirt with golf pants or shorts, while female golfers will wear a polo/collared shirt with a golf skirt, pants, or shorts.
A handicap in golf is an indication of what your score should look like in a full round relative to par. For example, if someone is a 10 handicap, you would expect them to shoot 10 over par for their average round.
As of March 2020, Rory McIlroy is the number one ranked golfer in the world. Brooks Koepka, Jon Rahm, Dustin Johnson, and Justin Thomas are also elite current players. Tiger Woods is also still on the PGA Tour and is widely known as the best golfer of all time.