in the beginning, for all practical purposes - biking shouldn't hurt. if it does you are either going too hard initially or doing it wrong (wrong fit, etc)
make sure that you do enjoy it. nothing is worse than doing something that you do not enjoy. psychologically that is half the battle. in the 1st year of training, you will experience the fastest gains in fitness of all.
fitness is not just a lack of training but an inadequate diet. you will start having a different relationship to food, i.e. looking at labels and seeing how this 'fuels' my rides, etc.
the body is an incredible machine, and will adapt quite nicely to most stimulis.
if you are going from 'losing it' to 'using it' you will experience soreness (legs, butt, arms, even facial fatigue) but eventually your body will adapt to the 'changes' you are throwing it. i'd go slow at first, almost laughingly so. the best exercise is the type you stick with, and failure rates are high if you start too fast and injure yourself or flame out before your body is ready.
as long as you are turning pedals, you will eventually get to where you are going - literally and figuratively.
i know you are probably looking for a set milage and times/frequency to workout, but beginners have such differing needs and are all over the spectrum that the best thing is to spin and learn to listen to your body.
after a base then we can fine tune you and pass all of us up.