The Assets tab shows all the assets currently in your project.
Lists all your projects assets.
Lists the models available to the project.
Lists the materials available to the project.
Lists the meshes available to the project.
Lists the textures available to the project.
Right clicking in the Assets tab gives you a number of options:
Opens the location of the asset in a file explorer.
Creates a folder to store assets in.
Opens a dialogue that allows you to import new assets to your project.
Refreshes the list of assets.
Deletes selected asset.
Exports asset as .mtpackage, which is a file that contains the asset along with all the required metadata files.