Server side rendering vs client side rendering and how does web sites used to work before angular

Im kinda new to the whole web applicaiton , and web sites world, but i started to programming and build my own web , using angular and i feel very comfortable with the idea of client side rendering , and the using of AJAX in angular($HTTP / $RESOURCE) , but i didnt use the "legacy" apporach to building web sites , because i jump on angular because it was sound like the best new !

but as i learned i got alot of obstacles in my path because lack of knowledage in the tradionial web site technoligoes and how all developes , i was like to know how the web sites has started , and what are the attuidue toward this world , and how does the server side rendering works , because as i understand all of this , is that simple i have templates , and the JS in the side client do all of the manipulation , add/delete divs etc , and there is no any connection to the server side about rendering the DOMS at all , only get information by using http or resources.. i want to know how does php server side works .