You can use the pkg_add to install a software package from a local file or from a server on the network.
pkg_add lsof-4.56.4.tgz
If you do not have a source of local packages (such as a FreeBSD CD-ROM set) then it will probably be easier to use the -r option to pkg_add. This will cause the utility to automatically determine the correct object format and release and then fetch and install the package from an FTP site.
# pkg_add -r lsof
The example above would download the correct package and add it without any further user intervention. If you want to specify an alternative FreeBSD Packages Mirror, instead of the main distribution site, you have to set PACKAGESITE accordingly, to override the default settings. pkg_add uses fetch to download the files, which honors various environment variables, including FTP_PASSIVE_MODE, FTP_PROXY, and FTP_PASSWORD. You may need to set one or more of these if you are behind a firewall, or need to use an FTP/HTTP proxy. Note that in the example above lsof is used instead of lsof-4.56.4. When the remote fetching feature is used, the version number of the package must be removed. pkg_add will automatically fetch the latest version of the application.
Package files are distributed in .tgz and .tbz formats. You can find them at ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/packages/, or on the FreeBSD CD-ROM distribution. Every CD on the FreeBSD 4-CD set (and the PowerPak, etc.) contains packages in the /packages directory. The layout of the packages is similar to that of the /usr/ports tree. Each category has its own directory, and every package can be found within the All directory.