The Gloom Stalker Ranger from Xanathar's Guide to Everything gets the Dread Ambusher feature at level 3, which says (pg. 42):
At the start of your first turn of each combat, you walking speed increases by 10 feet, which lasts until the end of that turn. If you take the Attack action on that turn, you can make one additional weapon attack as part of that action. If that attack hits, the target takes an extra 1d8 damage of that weapon's damage type.
Rangers also get Extra Attack at level 5 (PHB, pg. 92):
Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.
So, for a 5th-level Gloom Stalker Ranger, since both class features involve taking the Attack action, do I have to pick whether to make my extra attack with the Dread Ambusher feature or the Extra Attack feature (similar to how a monster with Multiattack has to choose "Multiattack" instead of the standard "Attack" action) or do I effectively get 3 attacks, like a level 11 Fighter (but only on my first turn, obviously)?