In Authentic mode you have no UI at all so there's no waypoints on the map and no helpful reticle to help you hit targets.
You can tag enemies with your binoculars to find out distance and they'll remain tagged for extra XP once dead but they won't show in the UI when you put down the binoculars.
My recommendation is to complete the campaign on Hardcore difficulty to get used to enemies, and get a feel for the realistic bullet ballistics. (Optional) Then go for some collectible achievements on Cadet difficulty just to get a learn the maps and where each objective is.
Also you can skip optional objectives as this is challenging as is.
It may be a sniper game but don't forget your SMG and pistol. Enemies you sneak past might join the fight if your cover is blown so make sure to cover your back with traps.