The forearm consists of two bones, the radius and ulna. It is important that you are able to locate these bones properly. Always refer back to your basic anatomic position and remeber that the palms are always facing out. This would make your thumbs facing laterally and pinkys facing medially. Your radius is the lateral bone of the forearm and is on the same side as your thumb while the ulna would be the medial bone closer to the pinky side.
The radius does not contribute to the elbow joint at all, that is pure ulna and humerus. The olecronon of on the proximal ulna articulates with the olecronon fossa of the humerus forming the humeroulnar joint.
The distal end of the radius is also about twice the size of the distal ulna. The head of the radius is proximal while the head of the ulna is distal.
Source: Mind of Aaron
The last few minutes of this video covers the forearm
Source: Self made with Netter