Once there you can check the boxes next to all of the tabs that you want to display across the top of the page. You can also re-order the tabs by clicking and dragging the three horizontal lines to organize the tabs in any order you wish. The tabs going top to bottom will display left to right.
Please keep in mind that if you have too many tabs checked, a plus sign (+) will appear in place of the last tab and will have the rest of the tabs that couldn't fit listed underneath it, like so:
Clicking "Reset to Defaults" at the bottom will revert your tabs back to the application's original state which is:
Customers, Invoices, Estimates, Tickets, Parts, Inventory, Calendar, POS, Leads, Marketr, Admin (in that order)