I have never worked out in my life, and now I find myself being a 21 year old woman, 5'2, and 240lbs!

My husband is also very overweight at 26 years old, 6'2 and 340lbs. We decided today that it was time to loose weight. I can't do it anymore and I am feeling really motivated...TIL I GOT TO THE GYM.
Wow, so many machines and things to use. Its a really small gym which I like.
On Saturday I go to meet with the own who is gonna show me all the machines and help me out a bit, but I wanted to also come here and get some extra help.
My husband said he thinks I should stick with Cardio for a few weeks before doing anything else.
So today I went, and was on the treadmill for 11 minutes at speed 5. I think if I read the machine right my heart rate was at a 201. I have no idea what all the heart rate stuff means...
Then I got off that and went on this thing called a Cybex Arc Trainer. I really could not figure out how to work it but whatever I was doing made my legs burn. I could only do that for a minute
Then I got on a bike and was on there for 10 minutes.
I wanted to stay longer but was not sure what machines to use...
So I guess my question is how long should I be staying on these machines for? My husband suggested 30 minutes. I think I can do it...
Any other advice to help me out would be great to. Thanks so much