NBitcoin, how to implement wallet restoration? How does it work?

at first sorry for my ignorance, I have little experience at bitcoin programming.

Im trying to implement a very simple wallet using NBitcoin library. I have done some work, but now Im stucked with wallet restoration function.

Lets say I have mnemonic private key, then I calculate its public key.

With public key am I able to track all transactions associated with this key? Even if I used multiple adresses? How its done(NBitcoin)? Any advice? Do I have to iterate throught whole blockchain and chceck signatures?

Thank you.

With public key am I able to track all transactions associated with this key?

A public key has two corresponding addresses: Uncompressed and compressed. I suggest only generating compressed public keys for simplicity. The relevant methods are Compress and Decompress here.

So, yes.

Even if I used multiple adresses?

Multiple addresses: Yes, you should track all of them.

Do I have to iterate throughout whole blockchain and check the signatures?

You should use SPV: Download a block, verify it, keep the headers, skip to the next block. Also you should keep the transactions that are incoming/outgoing. Writing the current block height to the wallet file is a good idea, as after you launch the wallet for the second time, you'll only need to download blocks and scan for relevant transactions after that block height.