By introducing paging, we have actually introduced a level of indirection: we no longer think of a (virtual) address as an absolute offset from zero, but rather as a relative quantity: va = (page, offset).

We think of each virtual address as associated with a page number and an offset from the beginning of that page. This is called using one level of indirection.

So each time a process refers to a virtual address (and of course, note that this is happening almost all of the time), the system must translate the virtual address to the corresponding physical address based on the PTs for that process.