Hi Vincent -
Please refer official MS Docs for Sales Invoices: learn.microsoft.com/.../sales-how-invoice-sales
You can also watch some videos on Youtube:
https://www.youtube.com/watch?v=4OEPY0r9mXQ
https://www.youtube.com/watch?v=a0qMCPiozsQ
Furthermore:
Whenever you use a Sales Journal (With A/C Type Customer) and/or use a Sales Invoice, on posting any of these documents, a AR Subledger (aka Customer Ledger Entries) and a General Ledger are created automatically. You need not do any additional journaling to pass your AR Subledger entries into the General Ledger or vice versa. The best way to check it yourself is by using the "Find Entries" button in Customer Ledger entries, you'll see that no matter what CLE line you pick up, each line will have a corresponding General Ledger created


Nonetheless, after you are done creating your Sales Invoice, as highlighted in one of those videos, you can try "Preview Posting" it by pressing this button. What this feature does it, it will mimic all the Transactional Effects that will be happening once the sales invoice in question has been sent for GL Processing. Pressing "Preview Posting" does not actually post your invoice on the general ledger
https://learn.microsoft.com/en-us/dynamics365/business-central/ui-how-preview-post-results

Hope it helps answer your questions. Do mark "YES" on the top if this answer helped you