A .DLL (dynamic link library) file contains executable code and sometimes also contains data (resources, icons, strings, etc).
Windows programs are usually .EXE files. The programs stored as .EXE files can load .DLL files and use (call) the executable code contained in them.
Several programs can use the same .DLL files. Also, many of the functions that Windows offers programs are offered as .DLL files, such as KERNEL32.DLL, USER32.DLL, GDI32.DLL (and many others). A program can load any of these .DLLs and use the functions available in them.
Many .DLL files come with Windows itself, and many are installed by programs. A typical computer's hard-drive contains thousands of .DLL files.
More information about .DLL files can be found at http://en.wikipedia.org/wiki/Dynamic_Link_Library
This tool helps you explore the .DLL files currently loaded by the programs that are running.
.
You can list the .DLLs by program - that means the first level of the tree represents programs, and when you expand a tree node (by clicking on the small plus icon), you will see the .DLL files used by that program.
The alternative is to list programs by .DLLs. Then, the first level of the tree represents .DLL files, and when expanding a tree node, you will see the programs that are currently using functions from that .DLL.
You can search for a .DLL or .EXE by typing the name into the Search box. After you type something in the search box, only the search results will be shown in the programs and .DLLs tree view - the list will be filtered so only the files that match your search are shown.
Bellow the tree view of .DLLs and .EXEs (programs) there is a panel in which some information is given about the file you select: name, folder, version, size, date of the file.
The Refresh button refreshes the information, in case it has changed.