Umm, yea... (man, this is a tough question to answer without sounding trite) ....
OK, say you have a table with one column called NAME. If you create an html file with an input type of text, called "name", you can post this information to a php script and have the variable called $name equal to whatever the person entered in the field.
Then create an sql string that looks like this (very simplified):
$sql = "insert in table (name) values('$name')";
$res = msql_query($sql,$conn); with $conn being your connection to the database...
and that's pretty much it. Your question though, really begs that you should do some serious reading before getting to work...