For now I'll focus on men's tennis betting, as women's tennis is an entirely different proposition and has about as much resemblance to the men's game as boxing does to fencing.
The men's tour is split into tiers of events, with the four Grand Slams of the Australian Open,French Open, Wimbledon and the US Open all offering double the ranking points of the second tier of events, the Masters 1,000 series.
Winning a Slam will gain you 2,000 ranking points, while as the name suggests it's 1,000 points for a Masters title of which there are nine, plus the World Tour Finals for the top eight players of the season according to the yearly race.
Below that come the ATP 500 and ATP 250 events around the world and there are also Davis Cup matches, which is the yearly team competition, which also provides ranking points and the top players will also play a number of exhibition events in the year.
The tiers below are the Challenger Tour, which isn't televised, but can be streamed and sometimes attracts top players who for reasons of form or fitness drop down a level and generally face players of much lower ranking.
The format for all of these events apart from the Slams (and Davis Cup) is the best of three sets, with the Slams being the only ones played over five sets these days.
The longer matches I find are more profitable to bet on and this is because you usually get a more accurate reflection of the respective abilities of the two players over longer matches. The three set format more often leads to shock results whereas it's much harder to take three sets from a superior opponent, obviously.