On a separate Server

Create a Certificate

In order to send Events from SharePoint to the RemoteEventReceiver, there needs to be an established connection via https. For that connection, a certificate is needed which has to be added to the server certificates in IIS and to the SharePoint Trusted Root Authority. In case there is no certificate available, a self-signed certificate can be generated via the IIS-Manager.
As soon as IIS knows the certificate, it has to be exported to a .cer file to publicize it to SharePoint. To do that, double-click the certificate and under Details choose Copy to File. In the new window click Next and choose No, do not export the private key. Click Next again, and select the first format (DER encoded binary). Now you just have to choose the file path you want to drop the certificate in and click Next. Confirm with a click on Finish. A small window opens so that you know the export was successful.

Create a Site in IIS

A new Site in IIS has to be created:

the application pool can be chosen freely, there is just one restriction, which is that it is compatible with the .NET CLR Version 4.0.
an https binding to a chosen port (default 8755 or 443) with the previously created certificate as SSL certificate.

The directory which is mentioned under Physical Path will be deployed in the following step.

Check the prerequisites for the RemoteEventReceiver on the Prerequisites page.

Deploy RemoteEventReceiver

The Service User to run the App Pool of the Remote Event Receiver requires rights on the FireStart Server in order to send requests to the FireStart API.

Copy the content of the Remote Event Receiver folder to the physical path of the IIS Site (with the default settings of FireStart it can be found under the path C:\Program Files\FireStart\FireStart Resources)

Miscellaneous

The machine has to be accessible from the SharePoint server over the configured port of the RemoteEventReceiver Site.

On the SharePoint Server

SharePoint has to trust the certificate the RemoteEventReceiver is hosted on. If the hosting certificate of the RemoteEventReceiver is valid, no further steps are required.
By using the following command in the SharePoint-Shell, SharePoint can be used to trust a created certificate. This works because the certificate will be added to the Trusted Root Authorities of SharePoint.

$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate2("export.cer")

New-SPTrustedRootAuthority -Name "PROLOGICS RemoteEventReceiver" -Certificate $cert

Note: This only works for SharePoint On-Premise. With SharePoint Online you have to use a public certificate in order to host the Remote Event Receiver.