Since Repbox is a fully customizable and user friendly system, there are two main ways that you can add an event to an opportunity. Each are simple and easy to do, follow the steps below.

Find the Calendar module in the top module bar, you will either see it with the other modules, or will need to select "All" to find it in the drop down options.

Once you click on the calendar module, you will be redirected to the User Calendar page. From here, you will need to click the "Add Event/ To Do" button towards the top right of the window.

Once this is selected, the "Add Event/ To do" window will pop up. Fill out the needed information.

Once the information is filled out, click the "Go to full form" button at the bottom right next to the "Save" button.

When the new window loads, you will see the full form of "Creating New Event." Scroll down a couple of blocks to the one labeled "Accounts" Here you will see a drop down option. Select this drop down and choose "Opportunities." Here you can either link the Event to a current opportunity or create a new Opportunity. 

The magnified glass allows you to look up the existing opportunity (Typing in the name of the opportunity yields the same results)
The (+) sign allows you to add a new opportunity from this window.
Once you are done with inputing your information, click the "Save" button to complete this process.

First, you need to go to the opportunity record you would like to add an event to. This is done by going to the opportunity module and either picking the opportunity from the list view, or searching for the opportunity using the search bar(s) in the module.

Once the opportunity is found, select the record you need. The summary view will load.

In the left middle area of the window, you will see a Calendar Events header section. This section is sandwiched between the summary of the opportunity and the related modules list.

Once you find this header, click the "Add" button. The "Quick Create Event/ To do" window will pop up. Fill out the needed information in the fields provided. (If you need to add more information, you can always click the "Go to full form" button).

Once you are done, click "Save" and the event will be added to that list within the opportunity calendar events tab on the summary view of that opportunity.