How to process order in magento and post it to sendle

There are 2 ways to post order to sendle

1. Post it at the time of order sumbit event in checkout process
2. Post it at the time of shipment creation event in admin

You can set it in magento shipping method setting in admin. You can see “Book Shipment On” with 2 option “Order submit” and “shipment submit” like the following PIC.