GTM is a tool website owners can use to add several tracking mechanisms to their site with one script insertion on the site. All other tagging mechanisms are added through the GTM interface, for example: Google Analytics, Facebook Pixel, etc.
It is also possible to track specific actions and events through GTM.
Due to the large scope of what is possible with GTM, pricing is variable and depends on what you prefer to track through GTM. Get in touch with me to get a quote.