What are Technical Machines? They are circular devices which are programmed to teach Pokemon certain moves. Starting all the way from the beginning of Pokemon, Technical Machines (TMs) have been used to provide better movesets for Pokemon. Each TM is programmed to teach only one certain move, and only once. The ability of each Pokemon to learn that move is limited as well.
In my old games, I would never use TMs, seeing as there was no way to reuse them again. Starting with Pokemon Black and White, TMs (and HMs) can be used multiple times, no longer needing to cross-breed your Pokemon that had that move. Another note on TMs is how the Pokemon you taught it has to be in a wide-ranging Egg group. This way, your Pokemon would be able to pass on the move to other offspring. It was a painstaking process, but the restrictions were undone, thus making ideal movesets one step easier to reach. Of course, there are still Egg moves which can be passed on by the father.
TMs are primarily found in the wild, by pressing the A button when adjacent to a Poke Ball sprite. They tend to be usually hard to find, making them more worthwhile to use. Pokemon Black and White take advantage of this trend to put some TMs up in Icirrus City, where the TM can only be reached during the Winter season.
Another way to get TMs are to defeat Gym Leaders, who will give you a TM after the battle with their explanation of why they used that move. Usually, it’s a move that is part of the Gym Leader’s strategy, and is very annoying to get through. An example would be Elesa from Nimbasa City. After you defeat her, you will get the TM for Volt Switch. In the battle, she uses two Emolga and one Zebstrika, all of which know that move. Basically, it’s a hit-and-run move, and the user will switch out with another party Pokemon.
In the Black and White versions, TMs were also given to you by the Seven Sages. This is what happens when you topple Team Plasma’s rule and beat the game. The Seven Sages are scattered, and each time you find one, they will give you a TM with a newfound respect for you, since you were able to rise above an evil alliance. There are about 90 TMs, but despite this overwhelming number, there are not TMs for all moves. This is because it would ruin the fun of only having certain Pokemon with certain moves. It also paves the way for good battle strategies; if all Pokemon knew the same moves, the only beneficial one would be Imprison, which stops the opponent from using moves they share. TMs cannot be recovered using Heart Scales, so if you decide to use this in the previous game, please be careful. To remedy this in the new games, just use it again, and carefully pick the move you want to replace.