The whole point of a pricebook is speed — once it's built, quoting and billing is picking from a list, not typing prices.
Add items to a quote or bill
When you're building an estimate, a job, or an invoice, the line-items step lets you add from your pricebook. Search by name, pick the item, and its description, price, tax setting, and rate type all come across automatically.
Set the quantity — the line total works itself out.
Adjust the price on the line if a particular job calls for it; your pricebook stays unchanged.
Mix as many items as you need — services and products together.
Note: Editing a price on one estimate or invoice only changes that document. To change it everywhere going forward, update the item in the pricebook itself.
Related: Create an estimate and Create an invoice.