Tokens are non-card items usually represented with coins post-it notes, or cards themselves. Unlike cards, if they are discarded or otherwise removed from the field (such as from a Blast Card) then they are removed from the game, essentially they stop existing. To put it simply, Tokens are things on the field, usually created by cards, which are removed from the game if they leave the field.
Like cards, there are multiple types of Tokens.
Rule Tokens change some aspect of the game, usually by modifying the parameters of play such as drawing additional cards, playing additional cards, or gaining a blank at the beginning of your turn for each of the token you have.
Point Tokens grant the owner of them points. See also: Point Card
These tokens allow their owner to take some action, such as discarding other player's cards or liquefying themselves into points. Among effect tokens, there are two types:
Tokens which are one-use usually require removing the token from play to activate the ability, or as a part of the ability removes them from play. This is useful for effects that are particularly strong, but that you wouldn't want the player to use multiple times. There may be additional costs in addition to removing the token from play, such as spending some amount of points or discarding a card from your hand.
Multi-Use tokens have an ability which has a restriction as to when it can be activated, such as paying a certain number of points or by tapping it (like in Magic). These effects are usually something small enough that it isn't busted if it is used multiple times throughout the game, such as discarding specified cards on the field but only once per turn.
In general, if there is a card for it, there's also a token for it.
Tokens have a variety of uses, usually related to what type it is.
Tokens can plainly say "Instead of paying points, remove this from the game", but more generally tokens can be used to track some resource that you have, with the added bonus of visually seeing the stuff you have.
- To tap something is to turn it 90 degrees. Anything that you control becomes untapped at the beginning of your turn.