Yes. You must add GA code for all the pages you need to track. You can only paste the code on the important pages that you want to track.
Hi, Put your GA code below the <head> and above the <body> and use this code every pages of your site for tracking.
if you want to track every pages of your website then your have to enter tracking code into every pages.
if u wanna track your site, put it to every page, but best would be to put it just before </body> in order to loading GA code doesnt slow down loading proccess of whole page.
Google Analytics code is placed between <head>...</head> on each pages which you want to track. Generally, footer or header file are same on each file. so put Analytics code in header or footer between <head>...</head> tag.
head tags are fine, but if you use a CMS like Joomla you could have a extension that fixes this for you.