When using project files, a usable version of the library is created in the directory specified by the Library_Dir attribute of the library project file. Thus no further action is needed in order to make use of the libraries that are built as part of the general application build.
You may want to install a library in a context different from where the library is built. This situation arises with third party suppliers, who may want to distribute a library in binary form where the user is not expected to be able to recompile the library. The simplest option in this case is to provide a project file slightly different from the one used to build the library, by using the externally_built attribute. See Using Library Projects
Another option is to use `gprinstall' to install the library in a different context than the build location. `gprinstall' automatically generates a project to use this library, and also copies the minimum set of sources needed to use the library to the install location. Installation