Cataln was made to ease the difficulty of knowing where to look to learn math. Although there are many popular resources such as KhanAcademy, after a certain point resources like that don't exist or are not well known. Thus it becomes increasingly difficult to know where to look for information on higher level topics especially for those who are not guided by a university. Those who do not know better to know where to look or even what to look for are stuck without much hope for finding the information they require. Cataln acts as a highway to help route individuals to where they should be going to obtain this information.
On the navigation page you can browse various fields in mathematics. These fields or organized by difficulty (elementary, advanced) which you may filter by. From there you can select Read More on your field of interest to explore resources!