First of all, I want to apologize for any English mistakes on this guide.

Nautilus is a champ who has always fascinated me. His hard CC (4 out of 5 abilites are CC!) and his tankiness attracted me since the first day. Nautilus is a really nice support if your team need tankiness or CC. And if not, he is still a really nice option to deal with some squeashy supports. Now I would explain his Pros and Cons.

Pros

Very tanky
Engages really well
He has a lot of cc
Poke with E
Nice in teamfights
He can escape if he Q a wall

Cons

Not too much mobility
Doesn't peel very well
Getting CCed on lane can be mortal for you
The other supp can engage easily once you have done it.

Passive

His passive is really important. Once you have engaged somebody, you stun him with an autoattack. Passive is useful too for peeling. For example, if their supp is gonna engage your carry, autoattack him. What if somebody is going to escape? Autoattack. This autoattack also deals extra damage so it helps you bursting.

Dredge Line(Q)

Your main engaging tool. Just don't miss it. It has a nice range and it's wider than Blitzcrank's and Thresh's hook, so it's difficult to miss. You and the grabbed would be put on a halfway position. Dredge Line can be used too to escape if you hit a wall.

Titan's Wrath(W)

It gives you a lot of tankiness and extra damage on autoattacks. Activate it always before engaging or if you are being poked.

Riptide

Nice for poking and bursting, it deals nice damage and slow. Try to hit the enemies with more than one "wave" for extra damage and slow.

Depth Charge

One of the best ults on LoL from my point of view. Ult somebody and, no matter what he or she does, he would be stunned. When you ult someone, wait until the stun ends to throw the Dredge Line for having him or her more time stunned. Really useful on teamfights.

Nautilus on teamfights can be really useful if used well.

TANKINESS: Naut provides tankiness to all your team and can receive a lot of damage while his teammates fight.

CC: Your E slows on area and ulting the ADC or APC on a teamfight can win it for your team.

ENGAGE: Ulting somebody or just using Dredge Line can be a really nice engage if used on the right enemy.

UTILITY: If you have Randuin's, Solari, etc. use them on teamfights for really nice results.

Thanks for reading this guide, I hope it was useful to you. It's my first guide, so if you notice any mistakes please comment them to me.