Match! identifies phases in a sample by comparing its powder diffraction pattern to reference patterns of known phases. Hence, it needs a so-called "reference database" in which these reference patterns are provided. The reference databases are managed in the so-called "Reference Database Library" dialog.
There are several options for obtaining a reference database:
Many users also have diffraction patterns of own compounds which are not (yet) present in the COD or PDF databases. Hence, it is desirable to use these patterns in phase identification in addition to the "normal" patterns. This can be achieved using the so-called "user database".
You cannot only use one or the other of the above-mentioned reference databases but also combinations of them. For example, you can combine diffraction patterns of your own compounds with the COD database that is installed with Match!.