Um what I meant was "Downloading this tool called SharePoint Designer 2013 (SPD) https://www.microsoft.com/en-us/download/details.aspx?id=35491" and use it with your SharePoint Online site.
SPD 2013 can be used for both Online and On-prem even though its name is 2013.
I'm mostly familiar with Online. I *believe* that if you want to do something that like you are going to need to make a workflow with Designer. At this point, it is a free download: https://www.microsoft.com/en-us/download/details.aspx?id=35491
I don't know much about it but there are plenty of people here that should be able to help! Good luck!
They all use odata.
This is the application /u/Ecanem is referring to. Load it up, type in the URL for the sharepoint address, login with your credentials, then create new lists!
Yes, you can add and edit workflows in SPO. Workflows is a built-in function of SP (outside of Microsoft Flow).
You'll need SP Designer to create and work with the workflows.
For lists (including calendar) it's under the List Settings option under "Permissions and Management" section ("manage workflows").
You can also add/associate workflows to lists (and sites) directly from SP Designer.
Yeah as <u>UpstateNYer</u> stated below, that's an the "out-of-the-box" workflow which can't be edited.
You might be able to use those templates as a starting point and customize using SPD (free) though.