Open Invoices and press New invoice.
Pick a client, or press Add client and enter their name and email.
Add a line for each piece of work, with a quantity and a price.
Choose the due date. Ledgerly suggests 14 days from today.
Press Save draft.
The draft appears at the top of the invoice list with the status Draft. Nothing is sent until you send it.
Taxes
Set a default tax rate under Settings → Taxes. Each line can override it, for example for work that is exempt.