A Power BI report is built from visuals, and every visual starts with fields. The Data pane on the right lists the tables in the model. Expand a table to see its fields: a Σ marks a number Power BI can add up, a calendar marks a date, and plain names are text.
Select a number on an empty canvas and Power BI creates a column chart showing its total. Select a text field next and Power BI puts it on the X-axis, so you get one column per value. Numbers are summed by default, which is why the axis reads "Sum of Sales Amount".
You can also start in the Visualizations pane: pick a visual type first, then drag fields into its wells, such as X-axis, Y-axis and Legend. Both routes give the same chart. The wells always tell you what a visual is doing, so get in the habit of reading them.