I would suggest that you start with a Check List that is composed of IT Disciplines and their related Capabilities or Sub-Capabilities that need to be tested. This will give you a basic understanding of “what” to test. (You can perform a search for “IT Disciplines” to find lists that you can work from.)
I also suggest that you collect “IT Deployment” related information…
– Product or System Build / Building Rules and Configurations
– Product or System Package / Packaging Rules and Configurations
– Product or System Distribute / Distribution Rules and Configurations
– Product or System Install / Installation Rules and Configurations
– Product or System Instantiate / Instantiation Rules and Configurations
– Product or System Initialize / Initialization Rules and Configurations
– Product or System Execute / Execution Rules and Configurations
Doing so will help you establish how to properly reconstruct what it is that you’re testing. You can search for “IT Deployment Framework” to find different options and references for more information.
I also suggest you have a clear lest of Features that are associated with the Product or System “Release” so that you know what to test.
Understand what Technologies you need to test.
Understand what Interfaces you need to test.
Know all Product or System related Components that need to be tested.
If the developers have done their job and created Unit & Module Tests, you’ll want them as a foundation for your own tests.
There’s much more, too. Testing is a big space.
I hope this helps.