Click New Delivery in the top right of your merchant portal. Enter all the required information and click Save. This will create a draft delivery that can either be sent out by itself, or bundled with other deliveries.
If you have multiple deliveries to enter, try the Import Deliveries button in the top right of your merchant portal, next to New Delivery. If you are running a Shopify store, you can export orders directly from your store as a CSV and import to Trexity.