Here are some clues to the workouts.
1 length (from one end of the pool to the other) is 25 meters.
Workouts are based on and written in distances (i.e. 50 free means 50 meters or 2 lengths of freestyle)
The multiplier: the number of times you will repeat something (i.e. 4 x 50 free with :15 rest means you will swim 2 lengths of freestyle 4 times with 15 seconds rest between each 50)
About rest intervals:
You might be used to swimming continuously without taking a break. It's probably not the best workout anyway but, this year you are going to get to know the concept of interval workouts. It turns out that rest intervals are a very efficient way to maximize your workout. Not only can you manipulate your heart rate (with intervals), but you can take the rest period to think about your stroke mechanics and plan the next repetition to improve some aspect of your swimming.
If you are struggling to keep up, let your lane-mates know... they can always switch to their weaker stroke or perform a drill that slows them down. As (someone) once said "Work on your weaknesses; Maintain your strengths" and, nowhere is this more pertinent than in swimming (A trivial improvement in body position or arm mechanics can reap huge benefits). And if you're being asked to slow down, feel free (for instance) to work on your backstroke - or close your hand and swim 'closed fisted' to improve your 'catch' - or hold your breath for the entire interval to improve your vascular!
RI = rest interval (the amount of time between sets)
SL = streamline (kicking position with arms about the head and hands together)
FT = finger tip (freestyle drill where fingers walk along water's surface)
with dive= it means you get out of the pool and dive
If you're not sure what something means, You lane-mates will be happy to explain.
12 x 50 kk 1'45"/2'= kicking only, swim 50 meters at at time. Leave every minute-forty-five or every 2 minutes.
Do this 12 times.
How to swim on an interval:
If the workout says 4 x 100 free on 2:00 then 2:00 (2 minutes) is the interval, this means that you have 2 minutes to swim 4 lengths of the pool and rest before you start again. If you swim the 100 meters in 1:50, then you have 10 seconds rest before starting the next one. The intervals are always written for each lane/ability level.