Board Views automatically set columns width based on cards quantity. However, you can manually override this setting by dragging column resizer:
When you increase or decrease column width, this width is remembered for you only. Note, that sizing does not work on smallest and largest zoom levels. Also it is independent of zoom level. When you set one-card column width and change zoom level — you still will have one-card width of the column.
List views look more like a table. Every column has a translucent separator. Dragging this separator adjusts column width.