I believe "anonymously" is a better fit than "secretly". Since every transaction is public and you can't hide the transfer of coins. What you can hide is the identity of the parties involved.
As for creating a wallet, you can run your own node, possibly having a hardware wallet (not strictly necessary but it helps).
As for getting the coins, I'd say you need to avoid centralized exchanges, debit card gateway payments, and anything that requires KYC. You also probably want to meet in person and pay cash. LocalBitcoin has been an option for years, just be careful and do your own research.
As for the address, you want to avoid messaging apps, unencrypted (or even weak encryption) protocols, and possibly show/share the address in person.
Additionally, there are services that "mix" your coins to make them harder to know their precedence, in a process very similar to money laundry in the conventional money world. Two famous options are Wasabi and Samourai wallets.