Scopes in PUBG all have a zeroing distance that is displayed when aiming down sights. If the given distance is 100 metres then that means your bullet will land exactly where you click up to that distance. If your target is roughly 200 metres away then you will have to aim a bit higher – learning exactly where takes hours of practice and trial by error, but paying attention to the zeroing distance makes the process a lot easier. Quick PUBG tip: you can also increase or decrease it with PgUp and PgDn.
You can also suss out distances using PUBG’s map. Each white square on the in-game map is 100m². Therefore, if you are in a long-range shootout, you can pull out your map, spot roughly where they are judging from landmarks, and count up how many white lines separate the two of you. Aim accordingly and you should be able to land that tasty long-range kill.