Oof. I'll do my best, but I will disclaimer: I am in S5, and so my knowledge of the game is somewhat lacking, as well as my ability to execute on my knowledge. I can offer a beginner's guide, of sorts.
First, I take Grasp of the Undying as my keystone. This allows me to even up or win trades during laning phase. It's useless past that, but I'm usually ahead by then. It's not a super big thing, but most tanks don't need Thunderlord's. Bonds of Stone works if you're not looking to trade or be aggressive, but it's pretty much useless in top lane.
Second, I exist for my team. I don't care if I win lane as long as I don't feed. I don't care if I die in a teamfight as long as we win it. I'm not looking to carry, I'm looking to protect my DPSers. You're not looking to be unkillable as a tank, you're just trying to protect your backline so they survive. If your friend is so squishy that doing that is impossible, then there's something else going on, a bad matchup or something.
Third, I choose when we go in. I usually have to lead the charge anyways, unless someone is making a pick. I'm usually pretty good about picking the right times to go in. This can be kinda tricky for some players, but I hear it becomes more common in higher ELO. Practice initiations, learn the best places/times to go in. Alternatively, if it's a defensive tank, learn who to prioritize with peeling.
I hope that helps!