If you are facing a cho'gall, he counts as a SINGLE warrior. If you are facing a team with cho'gall AND another warrior, you want to take the DOUBLE WARRIOR build.

For the single-warrior build, the focus here is to give you burst and allow you to control the frontline. For the 1 talent, you want to get some extra range when you use your E to escape to help you not only survive but allow you to attack from a safer distance when your frontline comes back to help you. At 4, "Bigger They Are" is key by helping your D trait to deal more damage to the enemy tanks/heavy healthpool heroes you should be focusing with your minigun to take the most advantage of your trait burst damage. At 7, take the grenade for extra range so that you can disrupt enemy positioning from a safer spot, the other option here is Relentless soldier if you are going against a team that has many heroes with cc in order to help give you some extra armor and surv. Laster drill at 10 is the go-to choice usually to help with zoning map objectives, Odin is also a good ult but it depends on the map - usually drill is strongest unless you're on Battlefield of Eternity/Infernal Shrines, then Odin would be viable for pushing. At 13, you want to take the overkill talent - when you cast your Q (overkill) you need to right click on the hero you want to focus on if in a team fight and whoever you right click will get focused while others take aoe dmg. The 13 talent gives you extra range for the aoe damage while the 16 overkill talent gives you 50% more damage to the person you are focusing with overkill. At 20, take the odin or drill ult upgrade talents depending on whichever you took at 10.

For the DOUBLE-WARRIOR BUILD
Again if you're going against a team that is cc or dive heavy, grab Relentless soldier at 7, and Armor Piercing Rounds at 16. This build focuses around building minigun-time for your burst damage with your 4 talent. So you want to use your D early and often as long as you can GET THE HITS since it only lasts for 3 seconds to begin with. Stay with your team and use D early and often to build that tiemr. Grenade at 7 otherwise for extra damage to separate their backline further from their frontline, laser drill for zoning, at 13, the minigun self-healing is ridiculous for your self-sustain if you've been successful with landing your minigun and building up the timer. The grenade does dmg based on heroes max health, further helping you burst down those health-heavy heroes.

Ability overview
Use your Q for waveclear, or to focus a hero (must right click your main target) if you take the later Q talents in single warrior build.

Your W is meant to be saved to disrupt the enemy team's positioning - either separating people from their main group or finishing someone running away. Practice your ability to re-direct people with this bomb in try mode please before running into games.

Your E should be used to safely engage if you direct it properly - you can E sideways in lane, giving you extra basic attack range and then when you pop D you'll land almost all of your attacks with minigun on the person you are going against. IF you're in teamfights, save E for escapes

Your D is minigun, the burst dmg to people based on health %-age. You should focus on attacking the warriors, tanks, azmodans, and anyone else with significant health pools. The goal with D is to put yourself in position to USE IT as often as possible as long as you can actually LAND YOUR ATTACKS.

Your R - Laser Drill ult should be saved to place on objectives ONLY when the enemy team starts to show themselves to give your team some extra zoning and light dmg. At 20, the extra drill talent gives it significantly more dmg and zoning value.