I do not understand how to determine anatomical positions. What is the position of the humerus to the ulna?
Additionally, if you are trying to explain the anatomical position of a body part by its relation to another body part, you will have to become familiar with these adjectives: proximal, distal, lateral, medial, anterior, posterior, dorsal, and ventral. These are the "anatomical terms of location" that describe where the body part of an animal is located in relation to another one. I bring this up because you mentioned the position of the humerus in relation to the ulna.
To describe this relationship, you will need to be familiar with the dichotomy of proximal vs. distal. For something to be proximal to something else, it must be closer to the center of the body. For something to be distal to something else, it must be further away from the center of the body. (Think of the words "proximity" and "distance" to help you remember the difference.)
So, because the humerus is located on the upper arm and the ulna is a bone of the forearm, we can say that the humerus is proximal to the ulna. It is closer to the center of the human body.
An explanation of all of the anatomical terms of location can be found at the link below.
You are asking about the humerus and the ulna and the relative relationship between the two. Both of them are major bones in the human arm. The humerus is the main bone that makes up the upper part of the arm. It runs from the shoulder to the elbow. The ulna is one of the two major bones in the forearm; the other forearm bone is called the radius. The ulna runs from the elbow to the wrist. The humerus and the ulna meet at a section of the elbow joint called the trochlea.