Hi guys, need some advises on training here. Total newbie here, just got a bike. The closest cycling club is 500 miles away, i will be riding on my own ALL THE TIME!. So, how should i start? I have plenty of time, my work allows. I can spend 3 days a week cycling, the rest for swin and run, i'm training for triathlon. How far should i ride? How hard should i ride? It's flat here, no hill at all.

Hi Vietcong, I do some triathlons as well so I definitely make my limited on-bike training counts when i do them. If you are doing 3 bike sessions a week then I would recommend doing 1 long ride (build up to 2 - 3 hours) a week at aerobic zone and 1 or 2 shorter rides with 30 - 1 hour at threshold pace. You can build up the threshold ride by doing something like 2 * 15 mins your first week. Then up the duration to 2 * 20 mins next week. Then up again to 1 * 30 mins, then 2 * 30mins etc. etc. A few weeks prior to your race, you should be able to do the actual race distance/duration at your threshold pace.
Don't forget to work on cadence. I like to keep my cadence at 95 rpm or higher. Should be feasible if there are no hills around you.

On your longer ride you may try some intervals where you increase the gear resistance and pedal at a lower cadence (~70rpm). This helps improve your muscular strength (as well it gives you another system to tap into if your lungs/heart tire out)

Just my 2 cents.
Don't forget to rest/recover in your training schedule! Very very important.

oh and feel free to repeat the same threshold workout/duration the next time if you feel like the one you are doing this week is too demanding. nothing wrong with building things up slowly.