Yeah you read it right. Basically, your proficiency bonus consists of two elements: your rank and your (character) level, which you add together. However, if your Rank in a proficiency is 0, you only add half of your level, instead of your full level. +2/+4/+6 are the bonuses for Trained/Expert/Master ranks, respectively, this is a reflection of how the proficiency system works in Pathfinder 2e.