What are primaries, conventions and superdelegates? Start Here explains how the US chooses its presidential candidates.

The US presidential election is coming up and both the Democratic and Republican parties are choosing their nominees.

The incumbent, President Donald Trump, has his challengers but he has always looked like a shoo-in for the Republicans.

The story is different for the Democrats, who started with a record 28 candidates and have been working their way down to just one.

The US system for choosing presidential nominees is unlike anything else in the world. It is convoluted, and not everyone thinks it’s fair. Start Here explains.