How do I claim my core on MetaMask?

Could you please elaborate on the steps I need to take to claim my crypto assets on MetaMask? I'm a bit unfamiliar with the process and would appreciate a detailed breakdown. For instance, do I need to connect my MetaMask wallet to a specific platform or service? Are there any fees involved in the claiming process? And how do I ensure the security of my assets during this procedure? Thank you for your assistance in guiding me through this.