Welcome the forum, you have picked a good place to learn. There are tons of knowledgeable folks on here that you will learn from as I continue to learn. As far as answers to your word question, I will try my best.
Saddle is the low spot between two peaks, from a distance kind of looks like a horses saddle. Big game animals choose to use these for crossings quite a bit.
Drainage is refering to the draw between two fingers, basically where all the water runs down during spring time.
Ridge would be the fingers I am refering to.
Ridgeline would be the top of the ridge, normally used when walking to and from the Peak of a mountain.
Hopefully this helps or somebody with better definition skills chimes in.