Usually you have already compiled and installed the program you want to convert to a T2 extension package.

Find and download the tarballs you need in a directory for that purpose.

At this point it is worth checking what the installation documents say. For example you may need to use configuration options like:

--enable-special-feature

Once you have downloaded the latest packages they are most likely not in the bz2 format. If you have slow internet connection and want to prevent a second download you may want to copy the tar balls directly into the archive. For example:

gunzip package.tar.gz
bzip2 package.tar
mkdir -p download/repository/package
cp package.tar.bz2 download/repository/package/