The following video provides an excellent demonstration of how latitude is determined from the North Star:
Knowing that the sun, at the spring and fall equinox and at high noon (the sun at its zenith) will be 90 degrees exactly above the equator, you can do the same thing with reference to the sun. Of course, in this case, you have to subtract your measured angle from 90 degrees because the equator is designated as zero degrees latitude. By making proper adjustments, this process can be used for determining latitude at other times of the year and the day. Mariners had and still have tables for making those adjustments.
The following video may be helpful. (Please ask further.)