The simplest way is to use the safe_mysqld which is found in PREFIX/bin. You can run it like this:
./safe_mysqld --user=USERNAME &
USERNAME is the name of the user you want MySQL to run as, even though you're starting it as root. You should make a new user called mysql and only give it ownership to certain dirs like the MySQL data dir which is where the databases live. Read the manpage for more details on how to do this.
There should also be a file called mysql.server, which is used to start and stop the server automatically. In the source distribution it's under the support-files directory, I don't know exactly where it is if you installed MySQL when you installed the OS. Check /etc/init.d. Assuming you find it there, make symlinks from /etc/rc[0|3|6].d to that file (ln -s ../init.d/mysql.server [S in rc3.d|K in rc[0|6].d]##mysqld in most cases, where ## is the order you want it to start as compared to other things which start automatically on your system).
Also check out the online documention, specifically reading the tutorial if this is your first time using MySQL.
