addslashes needed for db security? Hack proving web apps

Hi there, I am wondering how to make my application more secure. No I was reading in a mysql book, that chars like ' are bad for db PHP provides the function addslashes. Is this the way to check for bad entries a user provides? What happens if a hacker tryes to delete my db entries with a input like 'delete ... Are there any good articles on the web about checking user input, securing webapps against hackers? Thanx andy