When entering invoices, each line can be designated as taxable or exempt by using the "Tax" column. By default 1=Taxable and 2=Exempt, but you can edit the list of codes by going to Maintain > Default Information > Inventory Items > Taxes/Shipping. Just below the line items on the invoice you can enter a sales tax code that will determine the tax rate that gets applied to the taxable items. You can only have one sales tax rate per invoice. So if you have items that are taxed at different rates (such as liquor) you will need to make separate invoices.

If you don't know how to set up sales tax codes, there's a knowledgebase article How to set up sales tax. You can also look in the help. The main thing to understand is that you set up sales tax agencies such as cities, states, and counties, then combine those into a sales tax ID to get the overall tax rate.

To make data entry easier, I would also suggest you go into Maintain Inventory Items and set up some items such as Beverage (set the item class to Non-Stock Item) and Labor (item class Service or Labor), etc.. You can be as general or specific as you want, just do what works best for you. The purpose for setting up these items is because each item has a designated sales account and Item Tax Type (and price if you want it). That will simplify data entry because those things will be filled in automatically when you enter the Item ID on an invoice.