To be honest, when I first started out I thought certificates were a very overwhelming thing and mostly because I never messed with them. So if you are in the same boat, fear not. They are not that difficult.
I am not going to go into depth of what they are since this is supposed to be short and sweet, however I will point you in the right direction.
Generating Certificate Signing Request (CSR) – This is if you need to purchase a SSL cert. You will need to create a key pair which will be sent to a Certificate Authority (CA) or your middle man IT department.
Installing a Third Party SSL to be used by Qlik Sense – Note you need a .pfx certificate with an embedded key!
OpenSSL – I highly recommend getting comfortable using OpenSSL. It is an amazing command line utility to work with certificates. It is a necessity if you start working with NPrinting, QABDI, and QIB.
Last piece of advice, you usually have two things at your disposal to troubleshoot: logs and your browser.
In your browser click the icon near your url. In Chrome it is at the left of the address bar:
Click ‘Certificate’ and you will see:
Simple test to see if which cert you are using and that it is considered valid by your browser.