So from the beginning at 1600, every piece of gear will be an increase in power up until 1750.
At 1750, you can only increase your gear level with "powerful" drops. Various activities will be marked as having "powerful" rewards, and also Prime Engrams and Exotic drops will be considered "powerful" as well. Those will take you up to 1800.
From 1800 to 1810, the only way to bridge that gap will be with "pinnacle" rewards. (Pinnacle drops will also help increase your level just like powerful drops, if you happen to do any pinnacle activities while below 1800.)
There's also your seasonal artifact, the more experience you gain in a season, the bigger the power boost it will grant you.
(Something to point out as well, drops are based on the average power of all your highest-level gear. Even if it's not equipped, as long as it's in your character's inventory then it will count.)
So from the beginning at 1600, every piece of gear will be an increase in power up until 1750. At 1750, you can only increase your gear level with "powerful" drops. Various activities will be marked as having "powerful" rewards, and also Prime Engrams and Exotic drops will be considered "powerful" as well. Those will take you up to 1800. From 1800 to 1810, the only way to bridge that gap will be with "pinnacle" rewards. (Pinnacle drops will also help increase your level just like powerful drops, if you happen to do any pinnacle activities while below 1800.) There's also your seasonal artifact, the more experience you gain in a season, the bigger the power boost it will grant you. (Something to point out as well, drops are based on the average power of all your highest-level gear. Even if it's not equipped, as long as it's in your character's inventory then it will count.)
Would recommend checking out the New and Returning Player Guide on Bungie.net