1. Click on Products from the sidebar navigation.
2. From the drop down click on Collections.
3. Click on purple Create collection button in the upper right hand corner.
4. On the next page add the information wanted for the collection and then click purple Save button in the upper right hand corner.
5. Then go to Products main page via the link in the sidebar.
6. Choose the product you would like to add to the collection and click on the title.
7. Inside the product settings scroll down a bit until you see the Collections section on the right side. Click there and then choose the collection you want.
8. When done click the purple Save button in the upper right.