Uprisings are a new four-player group content introduced with Patch 5.0. They are meant to be a lite version of flashpoints with no cutscenes and all action. Each Uprising should take regular groups about ~15 minutes to complete at the easiest difficulty. They are only available to Level 70 players and can be accessed in three ways

Swtor2credits is your best place to buy swtor credits cheap and fast for years.

Via the Galactic Command system (can’t select specific uprisings, auto-queue)
Via the Group Finder (can select specific uprisings to queue but can’t enter with less than 4 players)
Via the Uprising Terminal in Combat Training section of the fleet (allow you to enter with less than 4 players and with companions)
Currently only Story and Veteran Uprisings modes are available. Five Uprisings are available with 5.0 launch and more are planned in the future along with Master mode Uprising that are more difficult.

Story Uprisings are meant for fresh level 70s
Veteran Uprisings are meant for players in mid-tier (234/236 rating gear)
Master Uprisings are meant for players in top tier (240/242 rating gear)
CXP Farming
Uprisings are meant to be a good place to farm Command XP. They give 160 CXP and 200 CXP base for completion on story and veteran mode respectively but the last boss also drops an Uprising Bonus pack for everyone (Story mode drops Small Bonus Pack which give 240 CXP). Add in the daily activity bonus (20% more CXP), the CXP you get from killing the bosses, or the CXP Bonus from the Light/Dark Victory State and you could see about 500 CXP every 10 minutes with a premade group earning potentially 3000 CXP an hour with very little downtime.

The five Uprisings differ slightly in length as well

Inferno and Fractured are the shortest Uprisings.
Firefrost is slightly longer.
Done and Dusted and Crimson Fang are probably the longest due to multitude of bosses that have high HP.

Never miss 8% discount code CHEAPSW8 for swtor credits from http://www.swtor2credits.com/ anytime!