Click New Delivery in the menu of your merchant portal. Enter all the required information and click Create. This will create a draft delivery that you can schedule when ready.
If you have multiple deliveries to enter, try the Import Deliveries section in the menu of your merchant portal. If you are running a Shopify store, you can export orders directly from your store as a CSV and import to Trexity.
Don't forget to print your labels after scheduling!