Wikibase is the name of the software that was originally written for, and is used by, the Wikidata project. Wikidata is the free knowledge base that anyone can edit. Its data is used by Wikipedia, its sister projects and anyone else who wants to make use of a large amount of open general-purpose data.
Wikibase consists of several components. You can find an overview on the components page.
You can file issues, ask questions and propose changes on the issue trackers of the individual components. It's also possible to ask for support via the Wikidata project: