The Store is a place where you can exchange in-game currencies like diamonds and coins for other currencies or characters. The Store has three sections:

The General Store, where you can exchange diamonds and coins for other currencies.

The Portal Store, where you can exchange tokens you recieve in Portal missions for characters and shards.

The Scrap store, where you can exchange the tokens you recieve for scrapping 1-Star characters to get characters and shards.

You can not use hard currency in the Store. The items available in the Store will change every 30 days, so be sure you come back and see what's new from time to time!