For the last 6 months I have been trying to wrap my head around Web development and understanding the diferences beetween client-side programming and server side programming.For the moment I only know the client side at an medium level(javascript/jQuery) but I am also interested in learning PHP and MySQl for server-side programming.
What are the diferences of client side programming and server side programming?
When do I use client side and when do I use server side?
Those a web developer need to know both to be effective in writing website?