First of all I would check rrd4j project home page and check some documentation. On the main page there is usage example of how you create the database and I think it's quite clear and no needed to be explained, since it would be copy+paste.
Now what about storing the information.. First of all you need to define how much and what type of data you want to store. For example in the project I'm working, we are aggregating data daily, weekly, monthly and yearly. You also need to specify what is the frequence of data collection: because it really makes difference if it's 5 seconds or 5 minutes.
You should also have a look at former rrd project homepage and ganglia, the part where you defining the RRD files creation, it will really help you to understand how RRDTool and data storing works.