For others who may wish to do this, here is how to do it.
I think the easiest option in WebPlus is to add a hamburger menu icon to your header and hyperlink it to a panel in which you create the menu. You can have the panel appear on mousover and disappear on mouse out. However, if it's for mobile use, you should set the action to mouse click to reveal the panel and mouse click outside the icon to close it.
Attached is a suitable icon that you can use. If you need to change the colour from grey, just open it in an image editing app and use the recolour option - basically, make a colour selection using the grey colour and then use the paint bucket tool to fill the selection with a new colour. Be sure to save out the new icon as a png in order to keep the transparent background.