I am reading about web analytic and came across GTM and GA.
It seems that GA is a service provided by Google which generates reports and statistics on website traffi
Google Universal Analytics captures and provides the actual analytics data to the site administrator. For basic page tracking, Google Analytics provides everything that you would need. For more advanced tracking such as events, Google Analytics provides the capability as well, but requires the developer to add in the event handling via scripts into the code base.
Google Tag Manager DOES NOT do any detailed tracking, it uses tags such as Google Universal Analytics to actually do the tracking. What it does provide is a way of doing advanced tracking outside of the code base. The advanced tracking is configured using the Tag Manager UI rather than coded in.
cross posted from https://trajano.net/2017/01/migrating-universal-analytics/2/