Jaybird, you go, girl!
You know the theory, as you say, but it really is only you that can put it into practice.
It's going to take you months of shuffle/walking before you can run for any length of time, but if you keep at it you WILL do it. I am only one of LOADS of people here who can say that with conviction because we've done it too. Bigger people, older people, less fit people, even wheezier people.
Get up off that chair now and go for a walk. That'll be your Day One.
see ya.
;o)