To quickly create invoice for a number of jobs, simply select necessary jobs using Shift (to select range of jobs) and Ctrl (to select jobs one by one) keys.
Click Create invoice on the ribbon.
If you selected jobs for different clients or with different currencies, than you will get a notification that invoice can not be created. In other case, invoice adding form will be opened, where it will be possible to make final changes before saving new invoice.
After creating an invoice, job payment status will be changed to Invoiced. After registering a payment over invoice, payment status will be changed to Paid. Please note that payment status can't be edited manually, only creating/deleting invoices and payments.