never exercise but starting now for the diet

Hello.

I have never exercised before, never went to a gym or something like this, dont do pushups or anything actually.

I just started a diet (this time is the one ), and of course I understand that I need to exercise, so I bought an exercise bikes, just installed it and started paddeling , and I feel 2 things:

1. really really weak after like 2 minutes of paddeling, but I think this is just becuase I'm outta shape and it would be better with time, right?
2. that only my lower body is working, and just a bit of my lower back - then how this is helping me? should I use some other machine instead?

the problem for me was that when I come home at the end of a day, i'm just too weak and sleepy for going out jogging in shorts or going to the gym, so this is why I purchased this thing, so I can just put on some movie and paddel away, but I want to make sure that this workout is helpful, is it?

thanks

someone?....

Well done for getting the exercise bike! If you haven't exercised before then you won't be able to do much at first, but you will be surprised at how quickly you will improve. Try to increase by a minute a day at first. It will firm up your legs, and exercise your heart if you get warm and breathless.
If you're very tired after work, why not get up half an hour earlier in the morning and fit your cycling in then? Then you can shower to cool yourself down before going to work.

Hey thanks for the reply.

I can't do anything before work because work for me is the army... I'm leaving home on my way to the base every morning at 5:30am...

one more thing: I have this neighbor which is looking pretty big boneded/fat/whatever you prefer but when you touch his stomach (he asked me to lol) or his arms you feel that this is just strong muscales.
I asked him why is it like this and he told me that when he was only heavy weighted, he started working out alot and he didn't lose weight - all of the fat in his body turned into muscales...

Can it be possible? and how can I avoid it (I wanna be in good shape but mostly look good )

thanks