GAP insurance solves one specific, narrow problem — but that problem is common enough, and expensive enough when it happens, that it's worth understanding clearly rather than dismissing or buying on autopilot.
A new car depreciates faster than most loans pay it down in the first year or two. If the car is totaled or stolen during that window, your regular auto insurance only pays out the car's current market value — not what you still owe on the loan. GAP insurance covers that difference, the "gap" between what you owe and what the insurer pays.
Any one of these widens the gap between what you owe and what the car is worth — stack a few together and the exposure can be substantial.
If you made a large down payment, are financing for a shorter term, or are paying cash, you likely have little to no gap between loan balance and market value — meaning there's not much for GAP insurance to actually cover.
Three main sources, usually in order of cost from cheapest to most expensive: your existing auto insurance company (often the cheapest, sometimes just a small addition to your policy), a credit union (if you're financing through one), and the dealership finance office (typically the most expensive, but the most convenient in the moment).
Some auto loans, especially through credit unions, include GAP-like protection automatically or as a low-cost add-on — check your loan terms before assuming you need to buy separate coverage.
Related: see leasing vs. financing — GAP coverage is standard on most leases, which is worth knowing before you evaluate whether to add it separately.