This website has what's called a "responsive template". That means it changes how the site looks depending on the size of your screen. Responsive templates are an alternative to maintaining completely different sites for computers and mobile devices, which is considerably more work. On a computer, the main menu is nearly the full width of the template and everything is immediately accessible. Waving your mouse cursor over the menu makes the items that have submenus drop into view so you can click on the items in those sub-menus.
But on a small screen, the main menu compacts down into a small icon that looks like a square in the upper right corner formed by short white lines. Touching that on your phone or tablet will present the top menu as a drop menu. On some mobile devices, touching the menu items once is the same as waving your mouse cursor over them on a computer. But on other devices that first touch acts like a mouse click, making it next to impossible to get to the sub-menu items.
Because of this, there is usually a second way to get to the choices in the sub-menus. For instance, "Edit My Profile", "View My Profile", and "Private Messaging" are all part of the Classmates Login module and in the MEMBERS sub-menu. The "All Members" list in the MEMBERS sub-menu is what you'll get if you click on or touch MEMBERS, and then there's another list on that screen for selecting the various member lists. "Private Chat" is in the MEMBERS sub-menu but also can be reached by clicking the user group icon in the bottom Chat window border. For those items that don't have the option of having multiple access methods, we have them at top-level choices in the main menu.
One other thing you won't find on a mobile device is scroll bars. Sometimes sliding a single finger will do the job, like with the main site window. But sometimes you need to use two fingers, like with the Chat window. This is pretty typical for mobile devices.
Not every aspect of this site renders well responsively. For instance, the tabs you see on the front page and in the Profile Editor do not resize or become menus. They simply do their best to remain useable and on a small screen can result in a lot more vertical scrolling.