How do I use my iCloud email for texting? It seems that with my computer, I can only send emails from my  iCloud account, but I want to be able to text on my computer from my iCloud account. How do I do this?
You can send and receive iMessages using the Messages app on your Mac. You may be prompted to sign in to iCloud if you haven't signed in using System Preferences. Enter a recipient and message to send a message.

You can't send SMS or MMS (commonly referred to as text messages) — this requires a linked iPhone with a SIM card and these messages are sent using the phone number.