When you evaluate an expression, the Suggestions Bar will normally appear after the output to suggest further useful operations:

To temporarily prevent the Suggestions Bar from appearing, click the minimize icon in the upper-right corner:

To resume showing the Suggestions Bar, click the arrow icon in an output:

To turn off the Suggestions Bar permanently, choose and uncheck Show Suggestions Bar:

Neither the Suggestions Bar nor the Show Suggestions Bar icon will be shown until the Show Suggestions Bar after last output checkbox is checked again.