Problems with keyframes when animating

Hello! This is my first time posting on the forum, and even more importantly, my first time really sitting down to learn Blender. I am trying to learn this so I can create my own models for use in Unity, and not have to worry about finding free ones or paying out a lot of money for this hobby. I am trying to animate a model I have imported from MakeHuman(as a .mhx), and I have had somewhat okay success. The first problem is that the animation, when played in Unity, is not smooth. Basically it is a walking animation, but instead of looking like a smooth, continous walkling motion, it jumps back to the first pose. Here are how the keyframes are set up:

1st keyframe: Character raises right leg a little, and right arm goes back.
2nd keyframe: character extend right leg farther, and right arm goes farther back.
3rd keyframe: Right leg comes back to standing pose, as well as right arm.
4th keyframe: Character raises left leg, left arm goes back
5th ketframe: Character extends left leg fully, left arm goes even farther back

This animation looks like the character is walking in Unity, but it not smooth/continuous. I do have the animation lopping continuously in Unity, it just looks ‘chopped’, if thats the right word. I am not sure what I am doing wrong here.

The second problem I am having, is when I create a keyframe, then create a seocnd one, it applies the effects of the second keyframe to the first keyframe. Here is an example of what I mean:

1st keyframe the character extends right leg.
2nd keyframe the character brings back right leg.
3rd & 4th keyframes the character repeats this, except with left leg

The problem is that the position of the left leg in the 3rd keyframe gets applied to the 1st keyframe.

I have no idea what I am doing wrong on either of these issues, and I would greatly appreciate some advice/help. Thanks for taking the time to read my post!

Sounds like you are forgetting the fourth dimension, time. If you don’t move the timeline the animation will have zero time, which means that when you are creating a new key for the same leg you are overwriting the last key, because it takes place in the same instant (The same frame). This is also likely why your animations look choppy in Unity, it’s made out of one single frame. The amount of frames will probably translate as the resolution of the animation in Unity.