Slot machines whether mechanical or electronic have reels, the number of reels can vary between slot to slot. The reels contain the symbols in various combinations and when you spin the reels they will stop leaving you with random combinations of symbols.
Usually combinations of the same symbols will be winning combinations according to the paytable on the slot machine and if you are lucky enough to get a winning combination you will win a prize.
3 Reel Slot Machines
Above is a diagram that shows a classic 3 reel slot machine. As you can see the reels are numbered 1 to 3. When you hit the spin button or pull the lever the reels move or spin to be more exact and depending upon how the symbols fall you may get a winning combination. Classic slots with 3 reels and 1 payline are still the most common sort of mechanical slot machine. 3 reel slots do not have to be classic slot machines, as there are multipayline slots available that have 3 reels.
5 Reel Slot Machines
Above shows a 5 reel slot with the reels numbered 1 to 5. Again, When you hit the spin button or pull the lever the reels move or spin to be more exact and depending upon how the symbols fall you may get a winning combination.
7 Reel Slot Machines
Above shows a 7 reel slot machine. This is a very rare number of reels to find on a slot machine and this number of reels is only found in electronic or video slot machines.
9 and 12 Reel Slot Machines
Just like 7 reel machines 9 and 12 reel slots are another rare gem; they only show one reel symbol per reel as a general rule. This makes them different to 3, 5 and 7 reel slots as they all normally show 3 images per reel at any given point in time. To make this easier to understand we have numbered the reels in the above diagram 1 to 9 so that you can see exactly how a typical 9 reel slot machines reels look. A 12 Reel game would generally look the same but would simply have one more row of reels.