The Bank tab controls the two numbers that define how big everyone's bankroll is, and what it's denominated in.
Share price (units)
The baseline unit value — 1 in this example. This field is grayed out and flagged "Never editable." It's fixed permanently the moment the contest is created and can't be changed by anyone, including the commissioner, for the life of the pool.
Starting bank (units)
How many units every entrant begins with — 1000 in this example. This field is flagged "Locks at pool start." It can be adjusted freely up until the contest begins, then freezes once the first pick is made.
This also explains the Max units per pick cap from the Format & Wagering tab (10× starting bank) — if a commissioner wants a higher max-per-pick limit, they need to set the starting bank correctly before the contest starts, since starting bank can't be raised afterward.