You buy premium content from the Store. This content varies and can contain new Mechadroid types and items such as coolant to reduce heat!
Buy with Battle Points
You buy premium content with BP using the right 'Buy' button. The cost is displayed above the button.
Buy with Frags
You buy premium content with frags using the left 'Buy' button. The cost is displayed above the button.
Checking your storage
You can check how many premium items you own of a type.
When you try to buy a premium item with frags and you do not have enough you will be promoted to purchase more frags from Google Play. You select an amount and follow the Google Play instructions. Frags will appear after a few moments.