Mounting: In terms on Unix environment means, adding a remote or external location to the hierarchical root path of the operating system at a desired point. It makes the handling of the files easy for the Operating system as it is not concerned with the actual location of the path, it can be on the local drive or a usb drive or on some remote machine around the world. It is the task of the underlying driver to handle these complexities, as far as the OS is concerned it is agnostic to this process. This makes things very easy for user or developers.
Caching means you store the recently accessed data, in some local location, which is relatively fast to access then the original location of the data in the hope that this data might be needed again in the future.