Clicking on a bar line with the Selection tool will select the bar line and open the Edit bar line menu where you can select a different type of bar line, including double bar lines and repeat bar lines.

When you move the mouse over a bar line, you will see a round handle at the top of it:

You can drag it horizontally to move the bar line and so resize the measures. This custom size is defined independently for each view (linear, page, or part view). The custom width option is now associated with the measures. If you change the page layout or add or remove measures, each measure will keep its custom width reference. Compose may however slightly adjust it when aligning a new system setup on the left and right margins. 

Clicking the X when it appears on a bar line, will delete any custom measure width adjustments.