Welcome to becoming a triathlete!  I hope you are excited about your first tri.  Good for you for getting started.

My last two tris were "snake" pool swims.  In each of them, the starts were five seconds apart--a person stood there with a watch.  One tri had you wait by the edge of the pool where they told you "go"--and then you either jumped, dove, eased, or slid in--the other tri had you get into the pool when the previous person started, and then hold onto the wall until they yelled "go" and you pushed off and started swimming (I liked the latter start better as I was able to slide in gently and get positioned).  On the first tri, diving and jumping and hopping in were all permitted. FYI, I dove in and immediately dislodged my goggles so I lost time adjusting them at the first wall. I won't dive in again.

You swim to the end of the lane, touch the wall, duck under the rope as best you can then and swim to the next lane end.  Until the last lap, when there is usually a ladder there for you to exit (beware a pile up at the ladder if it's crowded).

I found a lot of people aren't honest about swim times, but IMO it's better to be honest--since you are individually timed, it doesn't matter when you start your swim, other than you want to be through with your tri before they run out of beer at the finish tent.  You will pass, and you will be passed, during your swim. The rule is swim on the right and pass on the left, and you are supposed to gently touch the feet of the person in front of you which tells them you are going to pass them (the best rule is to wait and pass them at the wall, but that doesn't always work out).  I never had anyone touch my feet that passed me, and in fact, some people did try to swim right over me a couple of times.  I also had to be patient with the ones I was passing--I would touch their feet but when we got to the wall they would just keep going so they haven't read this forum!  Some of them took up more than half a lane and I just had to politely bull my way past them and hope they didn't kick me to death.

Be prepared for a lot of splashing, rough water (which if you swim mostly in a pool, you won't be used to), and people who backstroke, sidestroke, and breast stroke--the latter take up a lot of room in a lane, so watch yourself around their feet.  All strokes are permitted. Even walking is permitted in the shallow areas.  You  just can't hang onto the ropes and pull yourself along, or get help from anyone else.

I would recommend that your backstroking friend go towards the end as she or he will be a bit slower than the freestylers.  The rest of you sign up for your legitimate estimated times. You will probably go a bit faster because of excitement.  And feel free to rest at each wall--a lot of people do!--just move over and let the other swimmers go on by until you are ready to proceed.

If you cheat your estimated time and go out with the faster swimmers, you will run the risk of being bulldozed over by people who are determined that the swim portion of the event will make or break their PR.

One thing I can guarantee is that you will have a blast.  Keep us posted on your training!

Terry