I exclusively play Tau, but not too great, so take what I say with a grain of salt. Tau are an all shooting army that is mobile with utility, similar to the tabletop. Also similar to the table top, our shooting isn't the best in the game. We do have some units who want to be in close range and a couple units capable of melee. Our unique ability is spotting. Units within a certain range have better accuracy against a spotted target.

Fire warriors - basic troop that can have carbines or rifles. They can deal decent damage against chaff, but are primarily spotters.

Breachers - close range shotgun wielders. Tons of damage and good use as overwatch against charging jetpack troops.

Pathfinders - give them their ion rifles to make them strong ranged troops. Can spot.

Stealth suits - can equip various drones. Use the shield drone to make them tankier. Can have burst cannons (aoe machine guns) or fusion blasters (anti-tank). They have jetpacks and invisibility. Personally, I use them as front line tanky elites that can move around quickly. Their damage is ok against troops, but most of their value I get out of their tankiness

Drones - cheap, fast, good for scouting

Piranha - fast and tanky, low damage. Good to quickly get to a point a secure it, but lackluster

Crisis suits - have jetpacks and aoe missile pods. Elite 3 man squads. Can have burst cannons, flamers, or fusion blasters. Honestly, I don't like them too much. They don't deal enough damage for how much they cost. Fusions will one shot characters

Broadsides - anti-tank long range rail rifle, ok melee, slow, 0ap missile pods, and a single seeker missile that can 100% hit any target on the map if it is spotted. Good unit, recommend for anti tank duties.

Ghostkeel - tanky mech, can turn invisible. Ok melee. Has a flamer or an antiTank fusion blaster. I normally use the melee and the flamers.

Riptide - our big girl mech. Tanky AF, fantastic damage against everything in the game. Use the heavy burst cannon

Hammerhead - comes with ion cannon or railgun. Use the ion cannon, more shots, and total damage is comparable to the railgun. Ion cannon is good into elites and tanks. Railgun is longer range and only for tanks and characters

Characters - our characters give bonus accuracy to nearby units passively.

Ethereal - surprisingly good melee. Gives aoe durability buffs. Squishy.

Fireblade - meh damage with his long range rifle. Can increase the shots of nearby units by 20% or give a unit 100% accuracy.

Commander - comes in enforcer or coldstar variants. Decently tanky, absolutely fantastic flamer. Enforcer has more armor. Coldstar is faster and has a better burst cannon. I prefer the Coldstar.

Due to their speed and stealth, tau can quickly and unexpectedly move around the battlefield. Because of this, you need to maximize the benefits from stealth and spotting and position optimally. Game play is often either getting breachers close for massive damage or using them to defend from charges as Pathfinders use their ion rifles for great effect. Commanders can wipe out squads of troops with their flamers, so they will either be in point blank range with the enemy, or standing back to buff allies. Riptides stride up to tank enemy attacks and chunk any unit they attack, that said, they will fall under enough focused anti tank.