mysql_fetch_array() is in PHP since PHP3. mysql_fetch_assoc() is from in PHP4.0.3.
mysql_fetch_assoc($result) is is the same as mysql_fetch_array($result, MYSQL_ASSOC)
Both are in the manual under the mysql extension functions.
I'm not sure if this was any help, but I hope it didn't make you stupider.
Experience is something you get just after you really need it.
PHP Installation Guide