Where to install javascript code

Where do I install the javascript code provided by the thrid party website trackers such as https://www.statcounter.com/

I’ve used this service in the past when my blog was on “blogger” with no problems but am getting funny results now on my WordPress blog.

I have tried putting the code in the sidebar, footer and header. Also does anyone know if its necessary to install the code into every page or post you wish tracked?

Thanks in advance
Mark McClean
https://www.myebayadventure.com