You will find the Library in the left hand side bar (circled below).

Your Library will be prepopulated with different labels (in the above square).

Click on the Upload button in the top right hand corner to upload content into your library.

You can choose from the below options to upload content.

Click on New Label (in the bottom right hand corner) to create new labels and categories for your library. You can create as many labels and categories as you wish to.

Each time you upload content into your library you will be asked which label/category to save the content under.

You can add as much content as you need into your library.