Pod English 57: Scuba Diving

Scuba: self-contained underwater breathing apparatus
Did you catch my drift? = did you catch my meaning? = did you understand?
I'm treading water. = I'm not making any progress.
I'm out of my depth = It is too hard.
Let's test the waters = Let's experiment.

I was thinking of having a go at rock climbing.
to have a go = try something
Why don't you have a go?