this is an extremely high-level and general question. there are a lot of things you need to think about first, including: what do you want to accomplish with Splunk? what sort of data will you be indexing? what do you want to learn from it? how many users will you have? what is your budget?
if you're planning to deploy Splunk at your enterprise, you should work with your sales team (which will include a Sales Engineer) to help you plan your deployment.
a good place to get information is the Splunk documentation. i recommend starting with the tutorial to get a high-level idea of what's possible with Splunk:
http://docs.splunk.com/Documentation/Splunk/latest/SearchTutorial/WelcometotheSearchTutorial
here is information about creating dashboards and views (which is part of developing apps) for Splunk:
http://docs.splunk.com/Documentation/Splunk/latest/Viz/Aboutthismanual
here is some information about common deployment architectures for Splunk:
http://docs.splunk.com/Documentation/Splunk/latest/Deploy/Architectureoverview
the rest of the Distributed Deployment Manual will also provide good info about what's possible.
