If you have not yet connected OnBuy with Shiptheory and set your order download trigger status, refer to the OnBuy setup guide here.
Once connected, orders will download into Shiptheory when the status of the order is modified and the order status matches your trigger status. If you have not yet set up any automatic shipping rules, the orders that download into Shiptheory will be sat untouched in the All tab.
From this tab you can view the shipment and book it manually to generate a shipping label by clicking the View option from the dropdown from the shipment in the dashboard.
Alternatively, you can setup automatic shipping rules so that you never need to login to Shiptheory, and all the shipping label, tracking number and label printing work is done in the background, based on a formula you setup. For more information, see the automatic shipping rule guide.