Delete completely gets rid of a column. Columns to the right of it all move over. So if you deleted column D, column E would become column D.

Hiding a column makes it disappear from view, but it is still part of the spreadsheet and can be hidden. If you hid column D, you would still see column C and to the right of it would be column E. You can still use cells in columns that are hidden in formulas.

This is a distillation column that doesn't have a continuous feed. The material that is to be distilled will typically be in a round bottom still at the end of the column.

Usually used for making a still, a reflux column distributes fluid or gasses to a variety of different locations.

New columns will always be inserted set at the default width. You normally select an existing column before inserting a new one, but no matter what the width of the selected column is, the new column will still be the default width when it is inserted.

No. You can remove the entire column with the steering wheel still attached.