Eclipse has automatically added in what you see on the left here.
First of all we have the name of the package, which will eventually uniquely identify Wedding Logistics on Google Play.
Then we have the import statements. One analogy for these is academic references - if you write an essay which doesn't show the sources for your statements of fact then your readers will think you're making it up. Well, think of your app as a very sceptical reader - unless every statement is ultimately backed up in a reference [unless every method is in an imported library], it won't believe you [won't be able to execute that method].
The import statements I have already just cover me for the basic operation of the Android Operating System, and for the initial Activity that I'll get to in a moment, so I'll be adding a few, to deal with the Context (the situation on your Android), the View (what's on screen), an OnClickListener (to notice when, say, the user clicks on a button), deal with Buttons, Toast (messages that appear temporarily on screen. So called because they pop-up, I think), and a DatePicker, &c.
I've got the outline of my list from the excellent hackaday.com Android Tutorial and then added one for the DatePicker. Eclipse helpfully highlights all of the import statements I'm not using at the moment
(see the little row of symbols on the left?) so I can remove any unnecessary imports once the code is finished. Equally, as I expand the app, I'm likely to need to add more imports to cover new features.
Then we declare a public class called WeddingLogisticsActivity (henceforth abbreviated to WLA), and that it extends the core Activity.
Just to unpack that a bit - public means that other processes can refer to WLA; class - well, for a full definition of that I'll give you the wikipedia article, but the short version is that it means I could have several examples of WLA, based on the definition of it given here.
As to the bit about extending Activity, well, the Activity is a core Android class which handles some basic stuff for me - saying WLA extends Activity is a way of telling the system I want WLA to start with all the attributes of Activity, and then I want to give it some more.
At present, all WLA does which is apparent to the user is load the screen from last time; however, if the user attempts to enter the date, nothing will happen. If they click Done, nothing will happen. Unfortunately, I'm out of time, so I'll get to rectifying that next time!