SkyDrive is now OneDrive, and SkyDrive Pro is now OneDrive for Business. Read more about this change at From SkyDrive to OneDrive.
OneNote Online was formerly known as OneNote Web App. Word Online was formerly known as Word Web App.
This short video provides highlights on collaborating on documents. As part of collaborating on documents, some of the things you may want to do is work together on a document using Word Online, track changes in a document being reviewed, access your documents from anywhere, or perhaps share a notebook on a team site.
To learn more about collaborating on documents, see Document collaboration and co-authoring.