What is a Binomial distribution and when, in an exam, should I use it?

The Binomial distribution is a sequence of N trials which each have a probability, p, of occurring. Each trial is either successful (with probability p) or not. It can be used to give us the probability of certain events occurring (e.g. three heads out of five coin flips, four broken computers out of ten)
So, you should look for three things in an exam question to use a Binomial distribution:a specified number of trials;a probability for each trial being successful or not; andonly two outcomes (e.g. heads or tails, computer working or broken).
If each of these three things apply to your question, use the Binomial.