is this okay for now

okay so i just started exercising and because its so cold here i have been just riding on my bike for about 15mins twice a day sometimes 3 i would much rather be outside walking though cant wait til this weather breaks but for someone like me who before this week never ever exercised is this a good start my main concern right now this point at my journey is to work on my legs and tummy is the bike a good tool for that also and about how many calories should i be burning a day i only intake about 600-800

You are doing fine to start.  I have a treadmill that I need to start using when I can't go to the ymca.