Every problem on this sheet carries or borrows, and each one has small ruled boxes above the columns for writing the carried digit. It is a scaffold: it gives a student a fixed place to record the regrouping step instead of squeezing a tiny 1 into the margin.
The scaffold is meant to be taken away. Once a student is recording carries reliably in the boxes, move to the plain regrouping page - a student who always has the boxes never practises doing it without them.
Writing the digit you carry into the next column, or the 1 you borrow. A dedicated box keeps that step visible and in line, which is where a lot of regrouping mistakes come from.
Yes - this page is set to Regrouping Only, so every problem carries or borrows. That is the point of practising with the boxes.
When the carries are landing in the right place on their own. The boxes are training wheels; leaving them on forever prevents the very thing they are meant to build.
Yes - on any addition or subtraction page, turn on Carry boxes under Layout help and set Regrouping to Both.