Cosmicubes are special items that have themed cosmetics you unlock via a branching path! Here's a handy guide on how to get and unlock the contents in them if you're new to the system.
1. First, you'll need a Cosmicube. To purchase a Cosmicube with Beans or Stars you will need to go to the in-game store via the Shop button on the left side menu.
2. Once in the store, click on the Cosmicube button at the the top side of the bar to right select from various Cosmicubes you can purchase.
3. Once purchased you want to be sure that you have the Cosmicube set as "active." To do this go to your inventory by clicking on the Inventory button from the left side menu.
4. From within your inventory, select the Cosmicube icon in the upper right side.
5. Select the Cosmicube you'd like to get items from and select "Activate".
6. Once active, you will see a red banner over your active cube. This means you will earn currency (called Pods) for the cube as you play. For more info on currency, check this article.
7. Once you have enough Pods for items you can go to the cube by selecting "View Cube" from the menu.
8. Select the item connected to the "Start" path of the cube to unlock the item once you have enough Pods to claim them. The item will appear in your inventory.
Note that once you purchase/claim a Cosmicube from the store, it's yours to keep! You can take as much time as you need to unlock the items within it.