Tar
Tar is a command that can be used to make a lot of files or a folder of files into one file. This is useful for distributing sets of files!
A file that ends in .tar is a tarball. Tarballs can also be compressed and end in: .tar.gz/.tgz (gzip) or .tar.bz2/.tbz2/.tb2 (bzip).
[edit] 1 Unpacking a tarball
For .tar.gz/.tgz:
tar -xzf FILENAME
For .tar.bz2/.tbz2/.tb2:
tar -xjf FILENAME
If you want to have the command line list all of the filenames as it unpacks them, you can use the verbose option:
tar -xvzf FILENAME tar -xvjf FILENAME
[edit] 2 Making a tarball
You can also make tarballs out of a folder:
tar -czf TARBALLNAME.tar.gz FOLDERNAME
If you want a list of all of the filenames as they are packed, use the verbose option:
tar -cvzf TARBALLNAME.tar.gz FOLDERNAME