Select the chart in your PowerPoint slide
Click the Chart Elements button next to the chart
Check the Legend box
Choose the legend position if available
To move the legend, click it and drag it to the desired location
To format the legend, right-click it and select Format Legend
Adjust font, size, color, and other settings as needed
If the legend is missing, make sure the chart has multiple data series
For non-chart objects, create a text box and manually add legend labels and symbols