How do the reserve and the bid increment work?

The Starting Amount is the smallest first bid. After that, every bid must beat the current high bid by at least the Bid Increment. The lot page always shows the minimum next bid, and a bid below it is refused with that number.

A Reserve is the lowest amount you will sell for. Bidders see that a reserve exists, never the figure. Bids below the reserve are still taken, so bidding can build toward it; at the close, the lot sells only if the winning bid reaches the reserve, and otherwise it ends Unsold. Leave the Reserve blank for a no-reserve lot.

Once you click Open bidding, the starting amount, reserve, increment, window, and soft-close settings are locked. The only change allowed after that is extending the close, and that extension is recorded on the lot and shown to bidders.