After selecting the removable device to create the portable installation on, the setup program will show the components that will be installed. All components, including ones that cannot be deselected, will be shown. If there are no optional components at all, then this screen is skipped and installation begins immediately.
The developer of the setup package can indicate requirement relationships between components; that is: indicate that one component requires another. If component A requires component B, selecting A will automatically mark B for installation as well, while deselecting B will deselect A too.
A description of what the selected component is for, can be seen below the component list. This allows for an educated decision instead of a blind guess on a short component name.
The impact on installation size is also immediately visible, both in absolute size and as a percentage of the available disk space.
A checkbox labeled "Full Detail" appears at the bottom. When marked, the component list will expand to show all files that the component contains and the folders into which they will be copied. Shortcut icons etc. will not appear, as those will not be created for portable installations.
Next up is the license agreement.