From you question I gather you are talking about Rx drug product labels.
First write up the specific steps to install the software in a known and repeatable way. Once this is done it's time to move on to the meat of the process, your user requirements.
Provided you based your purchase on formal user requirements then you already know what you expect the software to accomplish. These requirements should include access and security expectations along with the specific requirements of the users. Next step is to develop tests that show each of your user requirement works the way you expect it to work.
If you are operating the software at multiple locations then a performance type test suite completes the process.
Before you place it into production ensure you have your written proceedures that manage security, business continuity, training, change process, and operation.
Wells