Someone help please!!

I've played this game a little a long time ago and i recently just got back, decided to create a new character in the new league and play. Everything was ok until i got to act IV, and now i'm struggling to defeat the bosses, they one-shot me almost all the time and i dont do enough damage, i have no idea whats wrong to my character, beacuse i've been following a guide and i even gote some uniques but i struggle so much, i died like 15 times to one of the boss. My character is a ranger, i dont know its a bad class in the game, can somebody shed some light on whats wrong please?

Act IV is harder than the previous Acts. You should link your gear and tree people will be able to help you more. If you are following a good guide you should be in good shape. Most people won't have enough life or capped resists so make sure you have that. Also in Act IV there is high amounts of physical damage, as a ranger that is going to be harder (unless you have an IR build). When you get the boss mechanics down it gets a lot easier.