I agree that without an instructor it's very hard to get the full benefit, especially if you are somewhat inexperienced generally speaking.
But, that said, it can't hurt to talk about it.
I understand that the form is a straight spine, but my question is, how do you keep it?
Movement. If part of you misaligns or threatens to, reallign the rest of you.
I mean, shouldn't you breathe with it?
Don't understand that one.
And, how does the Form apply to fighting?
Rommel is correct about the balance implications. I would also add then when you have form, you can generate power in your movements, and you can move in any direction.
So movement and form facilitate each other. Relaxation gives you sensitivity so you know where to move, and breath work helps you relax (and think in my case).
Also, there are 2 forms - ball (rolling) and stick. The spine is straight in both, ie not twisted.
Both types of form have standing and grounded applications.
This won't help you much until you do the work with a good instructor/training partner, but maybe with that you'll get something out of this.