How do I record stock I buy from a supplier, and does it update my stock count?

Yes. Use Inventory → Suppliers and Inventory → Purchase Orders:

1. In Suppliers, click + Add supplier and enter the name, contact details and lead time.
2. In Purchase Orders, click + New purchase order. Pick the Supplier, choose Receive into (a warehouse or store), then add product lines with the Ordered qty and Unit cost. Click Create draft.
3. Open the PO and click Mark as sent when you place the order.
4. When goods arrive, enter the accepted and rejected units for each line and click Record receipt.

Accepted units are added to that location's stock. Rejected units are recorded but never added. A part delivery sets the PO to partial, and you can receive the rest later. WCart does not email the PO to the supplier, so send it to them yourself.