Have 2 iCloud accounts in my mac and don't know how
I have two iCloud accounts on my Mac (and in fact, most of my selected iOS devices) because of the way Apple IDs work. 

One of them iCloud accounts is used for iCloud syncing, etc and the email address attached to it is not of an Apple-owned domain (e.g. @icloud.com, @me.com). 

The second iCloud account is most likely your iCloud email account.