Customize the number of columns shown for each screen width.
The order is important and the first line should always have the largest number and the 'At least' setting.
This affects the product list, ( product categories view - product archives ), and all other locations, eg Related Products in single view, Products sliders (shortcodes), where the value is not overriden by the individual location settings.
In cases where there is only one setting, e.g. for the number of columns in a products slider, that settings overrides only the initial (the At least...) setting for the grid layout.
So if for example you create a product slider and set the columns in the Element's settings to '6' and you have in your theme settings the values shown above, when the screen width is larger than 1201px, the columns will be 6, when the screen width is smaller than 1200px the columns will be 3, smaller than 992px the columns will be 2, and so on.
You should choose these values with consideration on how your product images show in various screen widths, in relation to your settings about sidebar visibility, and site's grid width. Leave the defaults if you are not sure.