Win32® refers to the Microsoft® API available on its Windows® operating systems (Windows 95/98, Windows NTTM, Windows 2000).
In Win32, each process has an associated address space. Portions of address space can be reserved, mapped ("committed" in Win32 terminology), or unmapped ("freed") using the functions VirtualAlloc and VirtualFree. (In addition, NT allows one process to allocate memory in another process). File objects can be memory-mapped into the address space using MapViewOfFile. Various levels of protection can be applied to mapped address space using the VirtualProtect functions. On NT, ranges of address can be "locked" into memory using VirtualLock (and unlocked using the obviously named VirtualUnlock). The function VirtualQuery can be used to obtain information on a range of addresses (for example, whether they are mapped or not and what the protection level is).
In practice, most programmers will not need to manipulate memory using these functions as they will use the language's memory management (for example, malloc and free in C) instead. The commonest exception will be mapping files into memory.