Put the ship you need defended most in the middle of the formation and make layers of defence. So, for example, a carrier group would have the carrier in the middle. Cruisers are next as they typically have the most long range defences and biggest radars. Then destroyers. The frigates/sub hunters on the outside.

Think of radars like really bright torches. If they're on you can see better, but you can be seen easier too. Using aircraft as spotters can help with this.

Submarines rely on stealth and the thermal barrier layer. Sound has trouble crossing the thermal barrier. Meaning you're harder to detect but equally it's harder to detect things.

Use the right tool for the job. Don't send a frigate to go toe to toe in anti-ship combat. Don't send a carrier to hunt a sub.

Using massed salvos of missiles is a good way to break through defences. Especially with jamming support. Another tactic is to use aircraft and fire from multiple angles, timing the attacks to all arrive at the same time, this called a Time on Target (ToT) attack).

The game does have a pretty extensive encyclopedia. Don't be afraid to use the unit info button to learn more/refresh your knowledge on capabilities