HT/FT asks you to call the leader at the break and the winner at the end in one bet: Home/Home, Draw/Home, Away/Home and the other six combinations. Both legs must land — a team that trails at half-time and wins late kills a Home/Home ticket even though the final result went your way.
The market's appeal is price: combinations pay far more than the plain result, because you are pricing two correlated events. The correlation is exactly why bookmakers like it — most bettors overrate favourites to lead at both checkpoints, and the margin on nine outcomes is fatter than on three.
Draw/Home on a favourite at 4.75: the favourite must be level at half-time and then win. If it leads 1–0 at the break and wins 3–0, the more likely-looking Home/Home at 2.30 was the ticket that landed — HT/FT punishes being roughly right.