To save it, press it. If that has no result, long-press it. Then you should get a share menu and one of the choices should be to save it. (It should already show in Gallery, since it's probably stored on your phone's storage.)
To email it, tap the paperclip when you're composing the email, find the video file and tap it. You can't directly email a video that's in a text message. (Depending on the messaging app you're using, when you go to share the video, one of the choices may be to email it. That does both things at once - saves it and emails the saved file.)