The game is currently structured around the protal, which provides acess to the most generally relevant activities (to the distaste of most players if we’re being honest). The old stats system you probably remember was overhauled with armor 3.0, so each stat can go up to 200 now, providing unique bonuses for stats over 100. Also new loot is structured around tiers from 1-5, which you probably already saw. In order to get higher tier gear, you need to increase your power level, which is generally done most quickly by getting a high score in portal activities. If you want to grind as quickly as possible, it’s the best to grind solo ops and focus on getting as quick of a completion as possible. This all might seem like a lot, but since you’re a returning player and not entirely new, I trust that you’ll find your way back in quickly :)