This is the game part where you can spend your hard earned money to improve the performance of your bands. You can find it on top menu.
The first Shop shelf page shows all the available items that you can buy from the shop. Most of the items will improve one ability of band member. Also, it will add rating points to your manager rating, this will help you climb to the top of the managers chart. Buying and selling is done by clicking corresponding button next to item's information.
On the Vault page you can inspect what shop items you have bought and what overall bonus you are getting from items. You can sell items here as well.
The Upgrade vault page will let you improve your vault. Every upgrade will put your vault in upper level. Every level will let you buy additional shop items, gives some rating points to help compete in Managers charts. Every vault upgrade is done during the turn calculation.