Don't believe the lies
Gatwick is London’s second airport. It’s to the south, about 30 miles away, on the route to Brighton. As it is so far out, it’s not on the underground and black cabs don’t go that far, normally at least, so options are limited.
There are two terminals, North and South. There is a free shuttle that runs between the two and takes just a few minutes.
Gatwick is much smaller than Heathrow and it is easier to get around.
Heathrow (London Airport) is one of the busiest in the world. It takes flights from everywhere, and is a big hub for transfers. The airport is to the west on London, roughly 17 miles out.
We’re going to assume you are arriving here and want to get to central London (not really “downtown”) to a hotel or residence perhaps. If you are here for work, you may already have a car booked and this does not apply.