Definitions:
Page View means that a user has loaded (or reloaded) a page on your website.
User Engagement refers to how much time users spend actively interacting with your website or app.
It helps you understand how interested and involved visitors are with your content.
Session Start refers to the beginning of a user session — essentially when someone lands on your site or app and begins interacting with it.
First Visit refers to the very first time a user lands on your website or app using a specific device/browser.
Scroll refers to a user scrolling down your page — specifically when they reach 90% of the page height.