What I normally do (and did on my i30's) is as follows. This is because you CANNOT transfer waypoints from your computer to your car using the USB port and memory stick. In the case of KIA this has been confirmed to me by KIA customer services.
For a one-off
You set a route using the ultimate destination, then choose another destination you want to pass through - the sat nav asks if you want this to be a waypoint (via point) or a new destination. You can do this for several via points.
To Pre-Plan a route and save it for future use
I can also plan and save a route which uses several via points - via one of the options (on the Niro it's called Routes). I make this easy by first listing all my via points and destination in the address book.
It works fine, but for one big caveat. You are routed to each of the via points you have prescribed. If you detour round one the bloody thing will insist on you being routed back to it before it will plan the next section of the route. If this happens you at least have the via points in the address book to fall back on.
Another minor thing is that the forecast data displayed such as distance to go and time to go refers to the next via point and not the ultimate destination.
Whilst you cannot pre-plan a route, or waypoint on your computer and transfer it to the car via USB. On the NIro you can pre-plan points of interest and load them onto the car via a memory stick and then use the sat-nav to navigate to them one by one. But I have never tried this.
Before we go on holiday I use Google Earth or Garmin Mapsource to determine the coordinates of all the waypoints we wish to drive via or visit and load them into the address book via memory stick to the car. (This includes those times I want to force the car to take a road it would otherwise not chose itself). This makes it dead easy to create and save Routes.
The advantage of having Garmin Mapsource on the computer is that like Hyundai and KIA it uses Here Mapping and route planning software - so I am able to replicate on the computer the route the car will chose and add extra waypoints to ensure it follows the roads I want to go via. You have to own a current Garmin sat-nav with lifetime maps, then keep it and the computer up to date with map updates to do this. Mapsource has been superceded by Garmin Base Camp which is more simple to use but I have stuck with the old programme.
If anyone knows of other and better methods do please let us know - I'm all ears..
I apologise in advance if my terminology differs from the car itself - I am away from the car and can do this routing on auto pilot without really giving it much thought.