Before you get to Burlington, you will pass these exits in order: Waterbury exit, Richmond exit, Williston/Essex exit, then an exit marked "I-189 Shelburne".
You want the next exit, Exit 14W, route 2 into Burlington/South Burlington. Take the west-going exit towards Burlington.
The exits before you get to Burlington are the Colchester/Winooski (route 7) & the Winooski/Essex (route 15) exits.
You get off at Exit 14W, route 2 which is Main St (going west into Burlington) and Williston Rd (going east into South Burlington). You want the west bound "Main St/Burlington" approach.