So, I've been playing swtor now, however I don't know much how the gearing and armoring systems, and don't know what I should gearing myself with, I'm a sith assassin tank, any ideas on how I should go about this?

Truly Tanking and not just a Tank-spec with a DPS-build (Skank Tank)? You'll want your gear to focus on Endurance and Defense Rating, in addition to the ubiquitorious Mastery, which should drop from enemies as loot, just check the tooltips to see what the gear pieces do. Once you hit Level 75 and start earning Tech Fragments, you can buy gear from the Spoils of War vendor on the fleet that suits your class and spec, and use that to start raising your gear rating. Since gear ratings only move in increments of two - 270, 272, 274, etc. - and a character's rating is the average of their equiped gear, it can take a while to reach the current max of 306. I, personally, recommend reaching 306 before worrying about trying to collect an equipment set with bonuses (pieces of which can be found in Conquest Crates, Renown Crates, or bought from the class Tactical/Set vendors on the fleet).

What level is your character currently? If it is less than 75, just put on any piece that drops that has a green up arrow on it (replacing what you’re wearing).

What level is your character currently? If it is less than 75, just put on any piece that drops that has a green up arrow on it (replacing what you’re wearing).

 

I agree with this. Its not worth the hassle unless you want to craft new gear every 4 to 10 levels, also based on how high of a level your companion is. Get your comp to 20 minimum and you will do fine no matter what type of gear drops

this should help https://vulkk.com/2019/12/05/swtor-6-0-darkness-assassin-tank-pve-guide-by-ahz/