Import External Orders in to Sales Orders

Hi, I want to import orders from an external source into my sales order list in my desk and process these orders in same way as desk own orders.
Kindly guide me about the best way to import orders in ERPNEXT.Do I need to add custom code? describe the files where I need to add my custom code.
In short, I need guidance from where I start to do this?
Thank you

Either you can do using the data import tool or you can use RESTAPI

kindly explain a bit more or share the helpful link about RESTAPI.
I want to import amazon orders with the help of ECOMDASH API and show it to the ERP desk.

BTW amazon integration available in erpnext.

Here is link for rest api.

thanks for mentioning but I want to import orders from multiple market place not only from amazon. For this purpose I use third party api which provide the required functionality. Now I want to integrate this third part api in ERPNEXT for this i need some help and guidance to start this.