We'll take a moment to have a look at the project, which will differ in some ways to projects you have created just for the iPhone.
The first thing to notice is that you have more source code files than you are accustomed to seeing when you first create a purely iOS app. These are rather conveniently organized into groups in the Navigator pane as follows:
In the group named HelloWatch (assuming you used that name when creating the project) you will find the list of source code, xcasset, and info.plist files with which you are already familiar, and these files all make up the iOS app that will run on the iPhone. Remember, watchKit apps for watchOS need a companion iPhone app, however much the Watch app may be your focus, and possibly your user's.
There is little to add at this stage, and in this chapter we will not be changing any of the files in this group.