does anyone know any good reference on how to deploy code from Visual Studio 2015/2017 to Sharepoint Online? I haven't found any helpful information about it.
Any help would be appreciated, thanks in advance.
In SharePoint Online You can create Add-ins.
In SharePoint Online Farm trust solution is not allowed so only sandboxed solution can be developed and deployed.
You can create a sandbox solution locally and test, once done then upload to SharePoint online.Creation of Visual Web Part- Solution.
Sandbox code has been deprecated for some time. So Suggest you to go for Add-ins.
Waqas also mentioned this in his answers How to deploy Visual Studio project to SharePoint online site