Well done for taking up the sport, for which we will from now on assume is cycling I wouldnt worry too much about how you should be doing, just starting out. Frankly you should be sucking. As the other hubbers commented it depends on quite a few factors, mostly importantly being the terain (i.e. was it all hills / flat roud / tar road / dirt road ). Other factors, road bike / mtb, where you chilling to trying to go flat out ? I suggest just continue with your rides and then eventually build up to comfortably ride say 20-30km and then enter a race. It sounds very daunting ("race") but there always seems to be someone less fit than you at these events so dont be affraid. This will then be a good opportunity to assess how you stack up against other cyclest in terms of your ranking in the race. Later you will start to be able to judge your own improvement based on (1) improvement in your heart rate, (2) improvement in time over same distance (need at least 20km to be meaningfull in my opinion), (3) you will get to know your average speed over different terrains (i.e. improving from say 10km/h to 15-18km/h or more over general mtb terrain ... dont know road speeds) Hope this helps
