climbing specialists are rarely the best sprinters. different physiology and different anatomy.
at a start- find other riders who are faster than you are to ride with and spend some (but not all) of your time with them.
understand that both endurance and speed are only possible if you are fueling propery- not only on the bike but before and after. sprinting requires lots of muscle glycogen. the most important time for you to replenish your muscle glycogen is within the first 30 minutes after you ride. lots of folks like to consume chocolate milk immediately after a ride because it contains the 4:1 ratio of carbs
rotein. If you wait to refuel- say several hours after a workout, your muscles replenish less efficiently and you will have less to work with the nextd time you ride.
don't ride every day- give yourself a day off the bike and also learn about active recovery rides. you are not going to get faster/stronger without allowing your body to recover between stresses (muscles grow while they are resting after lifting weight, not during). Recovery rides are very low intensity (heart rate <120 bpm) for at least an hour (but my target is at least 40 miles). you are accomplishing a couple of things- increasing circulation/flushing out lactic acid out of your muscles. also you 'train' your muscles to spare glycogen in preference to using fat as a fuel source. you want your muscles to be as metabolically efficient as you can. be sure that you are sleeping regular hours and are well rested or you will not see an increase in your fitness.
ditto on alternating endurance and power or interval sessions.
learn something about training according to heart rate. Heart rate monitors are nice but are not necessary- I don't use them because I prefer to read my body to know where i am.
an endurance session for starters should be sublactate or what some call a tempo ride. You will see descriptions of your heart rate being about 70-80% of your max HR. you should be riding hard enough that your breathing rate should be high and deep enough that it's difficult to carry on a casual conversation without pausing to breath (but not hard enough to require that you are gasping for air). you can alternate 20 minutes tempo 10 minutes easy pedaling until your fitnessw improves enough that you can maintain that pace for hours uninterrupted.
an interval session might be sprint as hard as you can for a minute and then do a recovery pace for 3. repeat 3-8 times. alternately, gear to something that is comfortable to you and maintain a 100 pedal stroke/minute foot cadence. in 2 minute intervals gear up to a harder gear while maintaining your cadence. continue gearing up until you can't maintain your foot speed. do recovery pedaling for 10 minutes and then repeat. remember that the goal is to focus on rapid foot speed. don't focus on your speedometer as you are training but focus on your technique and the consistency of your efforts. the speed will follow
good luck and enjoy!