Collections section allows you to see the list of all added Collections:

Also, you can find the tabs in lower grid:

Details tab allows managing the following fields:

Products & Conditions tab allows adding products. You can start typing to search for the exact products to add and sort them.

Sort option  allows displaying products by the following parameters:

After sorting, select the needed product and use the arrows to move them.

move all products from details

move 1 product from details

move 1 product to details

move all products to details

SEO tab allows adding the following fields: