How to move, hide or edit your legend
When you have configured your visualisation, if you right click on your legend title you will have options to:
Change legend position
Hide legend
Edit legend...
How to show your legend
If you've hidden a legend but now want to unhide it, worry not!
Simply navigate the column you want to unhide the legend for and click the 3 little dots.
Then jump to the 'display' option as shown in the screenshot.
How to use legends with multiple marks
When configuring a custom visual, you will have the option of adding multiple marks to the marks legend, this can be done by clicking the 3 dots within each individual mark.
Once you have added each of your chosen marks to the legend, you need to make it visible at a visual level. This is done by clicking the 3 dots just under the custom tab.