Here's an example of a basic AR tank build:
level 1:
https://underrail.info/build/?AQgDAwkIAwYPDwAAAAAAAAsAAA8ADw8PAAAADwAABAhiK9--Temporal Manipulation psi is here just to make the game easier, can be skipped. At very early game you fight enemies with whatever gun you have (usually a pistol) until you get an AR. You also grab a metal armor or craft one around the Junkyard. When you have a stat point at level up, you should put one point in Strength to be able to wear Tungsten Metal Armor in future and one point in Perception to scale your Guns skill and damage better.
Suppressive Fire, Opportunist, Full-Auto and Concentrated Fire are core AR feats and should be taken when they are available.
level 10:
https://underrail.info/build/?CgkDAwkJAwY8DwAAAAAAPAsAADw8DyM8AAAAPAAALAhiKzsmVRVK374