Pokémon is a collectible card game. Namely for collecting. What started with 1 series has grown into dozens of series and mini sets to collect. Each series has been released under one main series. This main series is then further divided into subsets.
What series is my Pokémon card from?
To know which set or series your card comes from, look at the set symbol. Each set has its own symbol, except for the very first set, the Base set, which is not marked with a symbol.
The symbol is usually located at the bottom right or left of the map. An exception to this are the very first sets made by Wizards of the Coast. These makers had chosen to place the symbol to the right of the image. On the trainer or energy cards these are on the bottom right.