For this one, you'll simply have to park the trailer at a delivery point. For this one, you can do either the hard one or the easy one so long as you don't choose the "I'm in a hurry" option or skip it. If you're looking to get all the achievements, try to get this one at the same time as the "Like a boss" achievement.
Your goal is to line the truck up in the outline and detach it when the game mentions it's in the right spot. It may take a few tries to line it up but unless you're doing a speedy delivery or really falling behind, you'll have enough time to get it into position. Try to get somewhat close to the outline and make small movements with the truck to get into position. Remember that when backing up, left will push your trailer right and right will do the opposite. Try to gently nudge the trailer into position with small movements, as you're more likely to lose control if you try to sweep it into position. If you're on the easier option, you won't have to worry about it so much as it will usually be in an open spot that you can drive up to with minimal corrections so keep that in mind.