A Technical Machine (or TM for short) is a tool that allows Pokémon to learn new moves. In these titles, there is a piece of equipment installed at every Pokémon Center called a TM Machine, which allows Trainers to make their own TMs.
TMs can be made using League Points (LP for short) and materials dropped by wild Pokémon after battle. LP can be obtained as you advance the story or by trading in materials from Pokémon. Find moves you want your Pokémon to learn at the TM Machine and try making a TM!
The selection of TMs available for you to make grows as you continue your adventure. A single TM can only be used once, but if you have enough LP and the right materials from Pokémon, you can make as many as you like using the TM Machine. Think carefully about what moves you want to have your Pokémon learn to expand your strategic arsenal.