If you have no current bag or box equipped, simply right-click the ones in your inventory, and they will automatically load in their appropriate slots. To view your equip bag and box, open your character interface (Alt+C), click on the "Others" tab, and you will see where they are.
If you later acquire a better travelling bag or grid box, you'll want to remove the existing ones, as right clicking the new ones does not work if there is already a bag or box equipped. To do this, go to where you can view the equipped ones (Alt+C then "Others" tab), then you can drag them via left click to your inventory.
Important note: to unequip a travelling bag or grid box, a number of boxes on the bottom rows of your inventory must be empty. For example, if I want to unequip my Lv 7 Grid Box, I will ensure the bottom 7 item slots in the "Stuff" tab of my inventory are empty. I will then drag the Grid Box from my "Other Information" tab into an empty slot in the "Item" tab of my inventory.