To get an overview of Total War Attila's multiplayer aspect I've created this thread. You should be able to find the information you need to get started. Feel free to post question if you have any.
Factions
Alamans
Alans
Burgundians
Danes
Eastern Roman Empire
Franks
Geats
Huns
Jutes
Langobards
Ostrogoths
Sassanid Empire
Saxons
Vandals
Visigoths
Werstern Roman Empire
More coming soon
Commanding and moving your army
Total War multiplayer can be a hectic experience. To not be overwhelmed it's good to understand how to assume direct control, how to unlock the free debug cam and a few new Attila specific controls. Also, make sure you have Locket Group and Group on their proper key bindings, some attila players have reported these two being mixed.
Hidden stats
Attila have many hidden stats that they player can't see: rate of fire, bonus damages to horses or infantry, etc. Click here to find out how to find the hidden stats. Download the packetfile manager here. Once you are in the "db" folder, scroll down to "land_unit_tables", "melee_weapons_tables" and "projectiles_tables" for some of the more useful tabs.
Walrus Jones made a mod that give you clarity on many of the different hidden stats. Don't worry, this mod is compatible with all mods and Attila Vanilla. This means you can play multiplayer with all other people. Explained here.
A number of videos on the importance of ranged infantry, infantry, cavalry, moral, fatigue, general's abilities and other things. I'll take out videos that are irrelvant, and I'll also add important patch notes to indicate when the video was made:
Ranged Infantry
Archers and Crossbows vs Infantry
Crossbows vs Slingers and Archers
Ammo vs Cavalry
The Best Combination of Ammo and Abilities for Crossbows
Elite Crossbows Rek Elite Archers
Crossbows - Killing Infantry With Fire
Arrows, Ammo and Abilities vs Infantry
Testudo, Spaghetti Loose Formation vs Missiles
Upgrading Skirmishers
Slingers are..
Forest Cover Against Missile Fire
Loose Formation
Do Back Shields Work?
Burgundian Barbed Skirmishers
Loose Formation vs Cavalry
Friendly Fire
Ranged Infantry patch 2
Heavy Shot, Flaming Shot and Standard vs Infantry
Infantry
Infantry vs Cavalry
Pikes vs Infantry
Shieldwall
Shield Wall or Counter Charge vs High Charge
Axes vs Swords
Expert Charge Defense and Spear Wall against High Charge Infantry
Spear Formations vs Tagmeta Cavalry
Throwing Axes
Calling Dogs Back
Beating Elite Pikes Frontally With Cheap Melee
Infantry Formation Depth and Width vs Infantry
High Charge vs High Charge
Melee Attack and Melee Defense
Cavalry
Diamond Formation To Defeat Shock Cavalry With Melee Cavalry
Melee Cavalry vs Shock - Diamond vs No Diamond
Tagmata Cavalry vs Elephants , Cavalry, Spears and Dogs
Cavalry Charges in Forests
Cavalry Impact Damage
Horse Hewers vs Tagmata Cavalry
Cavalry Charge Speed
Side Effects of Flanking a Spaghetti Main Course
Moral
Stacking Fear and Morale Penalties
Positive Modifiers
Fatigue
Fatigue and Speed
Fatigue, Running and Time
General's Abilities
Brace on Cavalry
Brace on Infantry
Misc.
Why testing versus A.I. is useless
Unit Upgrades - What They Do
Unit Upgrades II - Which units to upgrade? - Protectores Domestici
Unit Upgrades III - Germanic Horsemen
Unit Upgrades IV - Hirdmen
Upgrading Several Units at Once in Multiplayer
~Wille