This is the British spelling of familiarize. It means to learn about something until it no longer feels strange, or to help someone else get there. You familiarise yourself with a new city, a set of rules, or a computer program; a teacher might familiarise a class with the fire drill. In everyday talk people more often say get used to or get to know — this verb sounds a little official, the kind you see in instructions and workplaces. American English almost always writes familiarize, with a z. In Britain you will often see this -ise ending, though some British writers still use -ize. It is the same word, said the same way; only the letters change. Taiwan exam papers and British-leaning textbooks tend to show -ise, so students meet this form a lot even when the American one is sitting next to it on the same page.