D,
You would be wise to heed the advice of expert Lakshmipathi
Learn the concepts first, worry about details later.
As always, your first reference should be help.sap.com. Try this link to start.
SAP Sales is a huge topic for someone new. Many of us have benefited from taking classes. Check out the classes found in this curriculum:
https://training.sap.com/in/en/curriculum/ss_som-sales-order-management-g-en
Best Regards,
DB49