Unsurprisingly, the use of Objects and classes are central to Object Orientated programming. You must understand the difference between the two clearly. So, we will start by revising this.
Please read the entire trail on Object Oriented Concepts.
Please read the trail on Classes and Objects. In this case, you should do the sections up to "More on classes", namely:
You should be able to complete these exercises also:
If you have the time, complete the trail on Classes. Inner Classes (the next section) are particularly useful, so well worth reading if you have the time.