The first time you use the inventory section, you will need to create a warehouse. This can be done by clicking on "Edit Warehouse" either under the "File" menu, or on the blue search sidebar on the right-hand side.
You will be asked which warehouses you want to set up. Check the boxes for the warehouse types you want to create.
Once you click "Create", the warehouse editor will appear. Give the warehouse a basic description (name) as well as address (if relevant).
The Last Inventory and Next Inventory date fields are for your information only; it is not used by OASIS for any inventory logic.
If you forgot to check a box to create a resell or consignment inventory warehouse, you can do so here by going to the "Tools" menu and creating the warehouse you need.