The Update() method calls the RemoveAllBlips() method, which removes any old UI RawImage GameObjects of cubes and spheres that might currently be displayed. If we didn't remove old blips before creating new ones, then you'd see "tails" behind each blip as new ones are created in different positions – which could actually be an interesting effect.
Next, the FindAndDisplayBlipsForTag(...) method is called twice. First, for the objects tagged Cube, to be represented on the radar with the rawImageBlipCube prefab, and then again for objects tagged Sphere, to be represented on the radar with the rawImageBlipSphere prefab. As you might expect, most of the hard work of the radar is to be performed by the FindAndDisplayBlipsForTag(...) method.
This code is a simple approach to creating a radar. It is very inefficient to make repeated calls to FindGameObjectWithTag("Blip") for every frame from the Update() method. In a real game, it would be much better to cache all created blips in something such as a List or ArrayList, and then simply loop through that list each time.