Google tag manager is a tool which helps you manage all your scripts (Google or non-Google) from one single interface like Google Analytics, Universal Analytics, Google Adwords conversion tracking , Doubleclick floodlight etc. To understand better about Google tag manager, this infographic would be helpful (Google Tag Manager, GTM, infographic, Introduction to GTM)
Google Publisher Tag is an ad tagging library with which you can build ad request. Google Publisher Tag takes all the details of ads and display the ads on web pages and mobile apps.
The Google Analytics 4 Tutorial for Beginners in 2023 can be found here. You will learn how to set up GA4 with Tag Manager, event tracking, and custom reports.