How do I filter data in looker?
Click the Custom Filter checkbox in the upper right: Enter a dimension or function. Looker will display a list of functions, operators, and field names to use in your expression. Click on a term in the drop-down to add it to your expression.
What is cross filtering in looker?
Cross-filtering makes it easier and more intuitive for viewers of dashboards to interact with a dashboard's data and understand how one metric affects another. With cross-filtering, users can click a data point in one dashboard tile to have all dashboard tiles automatically filter on that value.