It?s as simple as what u did in ur project. Execution of 
test cases is very simple if u knows how read English. But 
writing test case need to have a good knowledge of the 
application. When u are ask to write the test cases, you 
have to have the following steps followed.

1- Understand the Software Requirement Specification (SRS) 
thoroughly. If not able to understand, then speak with the 
domain expert i.e. ur Architect.
2- Take down the test points i.e. all the functionality of 
the feature.
3- Draw the Test Design Diagram or the Dataflow Diagram.
4- Check the possible path the feature will follow or the 
data flow.
5- Sort out which test case will be data specific.
6- Send the document for reviews to all the relevant 
persons.
7- Once the document is Reviewed & Rework and doc is in 
Approve state.
8- U can start writing the test cases from the Test Design.