Just another "start small" voice being added in here.
I was about 330 pounds when I started, and not at all active in the least.
Even beginning with 30 minutes would've been "too much" for me. Not only too much for my non-active body, but too much mentally. I never would've stuck with it!
So six months ago I started with 5 minutes a day. Every day. That was my goal. For about a month I stuck to 5 minutes a day every day. I even missed a day or two during that month, but didn't let it keep me from continuing. It was more important for me to build a routine than to push myself hard. After all, I could always add intensity, but I actually had to be DOING something in order to build it up.
After a while I added 5 minutes. And then in another month I added 5 more minutes. Keeping the focus on just getting up on my treadmill for x amount of time a day. I now do about 30 minutes of treadmill walking a day. I added a little intensity by going faster.
But this is 6 months after starting. It never would've happened at all if I hadn't picked a reasonable goal for myself. Everyone is different about what they can manage, but no amount is too small to start with!