This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
a) You used the wrong coordinates, so correct them
b) The artifact is not in Maven Central (or maybe it is, but not the version you want). Often the artifact is in another repository so you have to figure out which one and ad that to your pom.xml of settings.xml (or if you are using a repository manager such a Nexus, add that repository to Nexus)
c) The artifact is not in any repository. In this case you will need to manually add it to your repository using install:install-file (or deploy:deploy-file if you have Nexus)