Not sure what phone you're using, but generally speaking, when you have a picture open in the gallery, tap it and you should see some options. One of these will be a share icon (or this may be in a menu). The share icon is a dot with two arrows coming off it.
Tap the share icon or menu option and you should see a list of options, one of which will be e-mail. Tap this.
You should then be taken to a new e-mail in your e-mail app. The e-mail will have the image attached. You can then do what you would normally do with an e-mail.
Alternatively, create a new e-mail, tap menu, attach, select gallery and pick the pictures to attach.
