Looker is a piece of BI Software that metaphorically sits atop a database. It acts as an exploration, organization, and visualization layer for data in a database. Behind the scenes, Looker writes SQL to the database so that users of Looker don't have to actually know and write SQL themselves.
Looker is typically setup and maintained by analysts at a company, and once ready, allows others easy access to data, build and save reports/dashboards, customize visualizations, and more.
There's a lot to Looker, but three main components are:
The language that powers the setup and maintenance of a Looker account. LookML is typically used by analysts, and is the language that allows Looker to write SQL to a database behind-the-scenes.
Datasets that are surfaced to end-users for exploration.
Dimensions and Measures
By clicking on Dimensions and Measures in an Explore you can start to build-out reports and visualizations.