How can I set a waypoint between my starting location and my ending locat?

Use the Route Card

With iOS 10, you can use the Route Card to find nearby places, like gas stations, food, and more.

To add a detour to a trip, follow these steps:

1. Swipe up on the menu bar while you're navigating.
2. Select an option, like Gas Stations. Maps will show you a list of nearby suggestions.
3. Tap . Maps will add the detour to your original route.
4. When you’re ready, tap the blue banner at the top of the screen to resume your route.

To get detailed turn-by-turn directions, swipe up on the menu while you're navigating and tap Details. You can also see your trip overview and adjust your Navigation Voice settings from the same menu bar.

Selecting the output will determine where Navigation Voice will play the turn-by-turn directions . 1 If you’re using Maps connected to Bluetooth, like in your car, you can choose how to get these directions. Learn how to use Maps with Bluetooth.

Apple Maps has no simple method to have more than 2 addresses, 1 that you start from and 1 that you end at. It is not at all unreasonable to want visit another while on the way to your final destination, even if it is not gas or food that prompts it.

To accommodate your needs rather than Apples use a better different app.