Navigate to your Communication Site. (In the following examples, we will be using the Student Development site.) 

On your main page, there should be a webpart called Events or Calendar or whatever who ever created it decided to name it. It could look like either of the two screenshots below: 

Click '+ Add Event' underneath the title. 

Create your event. It is important to add a background photo behind the title to make your event stand out on the Trevecca Calendar site. 

Choose a Date and Time (required, the rest are optional) 

When you are done filling out the information, click 'Save' at the top. 

Go back to your main site and make sure the event populates in the web part.