Golem is a "Tank" unit, his main role is protect his allies by taking turrets focus.
Passive: I’m Right Here
Makes turrets prioritize this unit, in addition it will slow down when targeted to maintain the focus
Active: Shield Up
Grants additional armor to every unit on the field for a short period
Tactics: passive - Golem's go 1st and they run pretty fast unless focused, that goes well with his passive making sure he is the focused unit.
Use this unit to protect your frigile units mainly from "single target turrets"
active - "Shield up" can be a great boost to help the frigile units survive longer specially from AOE damage and lanes without Golem.