Three things worth knowing
Reels are the strips of symbols that spin and stop. A classic game has three; a game with feature rounds usually has five or more. The count does not make one game better than another — it decides how many ways symbols can line up.
Paylines are the imaginary lines drawn across the reels. Symbols that line up along one count. Some games have a single line, others have dozens, and the number is usually tied to the stake per spin.
The stake per spin is the figure you set before you press anything. It is the one number you fully control in this kind of game, and it decides how long a session lasts more than anything else does.
What a feature round is
Many games have a special round that opens when particular symbols appear together. It might be extra spins that do not draw on your stake, or a small game with rules of its own. Those rules are written on each game's own information screen, and they are worth reading before you start rather than during.
The mistake to watch for
Because a round finishes so quickly, the number of rounds played in a short sitting is far higher than most people estimate. The approach that works is to decide the amount for the session in advance and treat reaching it as the end, not as the point where you top up.
There is a step-by-step introduction in the slots basics guide.