There are two components to back up in a Sitellite installation:

1. The web site source files
2. The database contents

Assuming your web site document root is /home/you/www, you could create a simple backup with the following shell commands:

# backup the database contents
mysqldump --add-drop-table -p -u USER DBNAME > backup.sql
(enter password when prompted)

# make a tarball of the entire site incl. database
tar -cf backup.tar www backup.sql
gzip backup.tar

# remove the backup.sql file
rm backup.sql

# copy the tarball to a secondary/network drive
cp backup.tar.gz /path/to/backups

To restore from such a backup file, assuming the file has been copied back into your /home/you folder, you could say:

# unpack the tarball, overwriting the web site
tar -zxf backup.tar.gz

# restore the database
mysql -p -u USER DBNAME < backup.sql

# remove the extra files
rm backup.tar.gz
rm backup.sql