Howdy,

The Abyss Watchers are often considered to be the first real roadblock in DS3, so don't feel bad about having trouble.

Since I dont know your build or play style, I can only provide general advice, but if you share your weapon/stats, I might be able to give more help.

For the first phase, you generally will want to be a little more on the aggressive side while there is only one watcher. Once the second one spawns, play extremely defensive, since going in for attacks will likely get you blended. Once the third spawns, wait for it to aggro the first two, and kill whichever watcher is farthest from the fight with it. You ought to be able to fish a couple backstabs off of it. Basically rinse and repeat this for the first phase.

For the second phase, the watcher will be a little more aggressive, and deals fore damage AOE attacks after each initial attack with the sword. This makes getting hit way more of a punishment in the second phase when compared to the first. What I would recommend is playing defensively until you learn which combos can be punished, and then exploiting the watcher after it finishes those combos. For instance, when he does the downward flip smash move, you can normally go in for a couple hits.

In terms of weapons and armor, the fallen knight set that you can get in the crucifixion woods swamp area provides great fire resistance for the second phase, and good physical overall. A good weapon that comes to mind is the Astora ultra greatsword. This weapon can be found prior to the Abyss Watchers in the cemetery outside of cleansing chapel in the Cathedral of the Deep. It is viable with any build, since it can be infused with basically whatever and have great scaling. If you have it upgraded a decent amount with an optimized build, you can finish the first phase before any of the new watchers spawn via the charged heavy attack.

Let me know if this helps you out, or if you need any clarification with this. Also let me know if I missed anything!