It's a pool swim so this is usually a few people starting in each lane about ten secs apart. When you enter you'll prob give a prediction for the 500m swim so they put you with people roughly same time. If swimming isn't your strong point you'll be able to have a few secs rest at the end of each length
Sprint tri's are a great way to start - everyone welcomed and you do your own race with whatever bike/kit you've got. Age no barrier everything from 18 or so to 60/70+.
Bike kept in a secure transition where you will need your race number ot get it so will be very safe.
You do need a helmet (put on before moving your bike and kept on until you put your bike back in transition) and the other main rule is no iPods, etc - for safety reasons.
Overall, give it a go and have fun. Regardless of how fast you do it I'm sure you'll enjoy it. Anything else give a shout on here, I'm sure someone will answer.
Cheers