how do I view my iMessages from my mac

If you have iMessage enabled on your Mac using the same Apple ID as your iPhone/iPad/iPod touch.

Enable Messages in iCloud

Store your messages in iCloud so that you can see the same messages on all devices if you use Messages on more than one device.

For more details, see Access your messages on all your Apple devices.

Use Messages in iCloud - Apple Support

3 Best Ways you can view iPhone messages on PC / Mac (wideanglesoftware.com)