Learnlink and WEBCT are both learning systems that professors can use to post up lecture notes, quizzes, test scores, discussion boards for your class, etc.
It is up to the professor to use it... some prefer WebCT, some Learnlink, others use similar services like Moodle (moodle.org).
You won't know which your prof is using, or if they are using any at all, until your first day of class. So until then... wait until classes start and ask your prof
LearnLink you download a client/program from http://learnlink.mcmaster.ca
WebCT you login to online via the web (no need to download) at http://webct.mcmaster.ca