Your company decides to deliver the items ordered by the customer. This is recorded by creating a outbound delivery document (TCodes:VL01N, VL02N, VL03N, Tables: LIKP, LIPS etc).
Once the items are available for sending to the customer, you post goods issue which reduces your inventory and puts the delivery in transit. This will create a material document. You will post goods issue using VL02N but the material document created will be stored in tables MKPF, MSEG.
You will then create shipment document to actually ship the items. (Tcodes: VT01N, VT02N, VT03N, Tables: VTTK, VTTP etc).
You finally create a sales billing document. (TCodes: VF01, VF02, VF03, Tables: VBRK, VBRP etc). This will have a corresponding accounting document created that will be in BKPF, BSEG tables.
When customer pays to your invoice, it will directly hit your AR account in FI.
You will have to remember that these are not a required sequence. Some times, you may configure your system to create a SD invoice as soon as you create a sales order or you may not create a shipping document at all. This is the position where Functional Consultant would come into picture and study the company's order to cash process and configure the SAP system to do so.