After saving your library, you should be able to see your new part (along with the descriptive text we added in the last step) by expanding the library in the main Eagle window, and selecting the appropriate part name from the treeview:
But it's important to build up the right habits at the beginning, which is why we went into such detail in this tutorial. Learn to do things the right way now, and a future version of yourself will be very grateful, and you might even have a bit more money in your pocket avoiding a few board revisions due to poorly designed footprints!
Before sending out to fabrication, be sure to do a 1:1 print test! Print out a paper copy of the PCB design and place the part over the pads, checking that the outline, pads and shape line up. A magnifying glass is handy here
Like any complex software package, Eagle takes time, effort, and a certain amount of trial and error to master. We've covered the basics here in professional footprint design, but there's a lot more to be said about the subject.
But have a go at making more and more complex parts, be brave about putting your money where your mouth is having boards made, and most important ... learn from your mistakes! We've definitely made more than a few here, but that's the way you learn!
If you want to get all crazy on your footprints, you can also have a look at our other Eagle footprint learning guide: Creating Accurate Footprints in Eagle!