how to modification code in openmrs modules or platform

I installed platform 2.1.3 (Enterprise) and use Reference Application 2.8.0 using bitnami tomcat package now i want to modification some code is it possible ? if it is possible please help me how can i do this ? i am a beginner in this platform so please help me.

Thanking advanced

We customize openmrs core using modules. Please learn how to create your first module. You can the OpenMRS SDK to rapidly create, deploy and test your work.

Anyway, what did you intend to change in the core?

Thanks for your reply, i want to change dashboard design ,logo and i want to add some text and input field in patient registration and many others

is it possible ?

@farhad is this of help and