They can be seen on your Stats page under the last tab.
The tokens are a means of trying to curtail loot farming. Each level, such as Hall of Heroes, is broken down into a few different parts. As you progress through the level you will reach a certain point where you will earn a token for your progression. What they do is two fold; 1) they prevent obelisks that you have already activated in a level from re-activating without first completing all the tokens for that level and 2) they determine the chances a boss has for dropping elite items. If, for example, you tried to start Hall of Heroes at 1-3 and didn't have the tokens for 1-1 and 1-2, then GRNDL will NOT be able to drop epic items (or has a diminished chance to drop elites, but I have never seen an elite without all tokens, perhaps some one else can confirm).
So, they are not check points per se, since you can restart a level at any of the preset points, but they do make it so you can't just jump in at the boss level, kill the boss, get the loot, and then bail.
Come to think of it, the internet does have a million monkeys typing on a million typewriters and it is nothing like Shakespeare.