Certificates and keychains

I am a new iMac owner and I set it up myself and I am worried about the keychain, certificates and iCloud. Do I have to connect the certificates to the keychain. I erased, restored spent about 24 hours tryimng to set it up. Called apple to no avail, each tech was worse than the other. Forget about the genius at the store. Can someone help me with certificates and keychains?

Do I have to connect the certificates to the keychains ? And can I trust the icloud?

Thanking you in advance,

Sincerely,

Debbie