A simple way to create rounded edges to objects is to use a bevel node. It is a non destructive way to create bevel edges without having to add extra geometry to mesh objects.

1. Select the Render icon panel and switch to Cycles rendering engine. (Currently this node does not work with Eevee)

2. Switch Viewport Shading.

3. Split your viewport and select Shade Editor from the Editor Type.

4. Press Shift A followed by Input > Bevel (Or type in Bevel in the Search Bar)5. This will add a Bevel Node to the Shade Editor.

6. Connect the Normal purple dot from the Bevel Node to the [...]