I have heard of Instagram of course, but not sure exactly what it is.

Instagram is a dreadful site. There's no meaningful communication, it's totally shallow and superficial and full of attention-seeking weirdos and poseurs, and it has all the negative aspects of Facebook (as it is owned by Facebook), i.e. adverts for useless products that nobody actually needs, posts in a random order that makes no sense, and it only shows you a small proportion of what your friends post. It also demands to know your mobile phone number, which should be nobody's business, let alone Mark Zuckerberg's. I wouldn't touch it with a bargepole.