1 - silent hunter - all ranger spells you cast have the verbal component removed and don't break your stealth when you cast them.
13 - focused hunter - damage does not threaten your concentration on ranger spells or abilities.
17 - lethal hunter - you can use your Concentration to Focus on a target you can see when you activate this ability as a free action, you have advantage on all damage rolls you deal against a Focused target, if you drop your Focus on a target you cannot Focus on them again for the rest of the combat.
20 - master hunter - when you use your Focus it targets all opponents you can see, you may drop and reapply Focus as many times as you like against a target during combat.