In general it's a basic basic two step process:

Right click on the image and save it. (Make note of the location)

Using your e-mail client locate and attach the saved image to your e-mail, and send it.

DA

on the actual image you are wanting right click and select save image as when the dialog box opens select where on your pc you want to save the image to like desktop or in My Pictures folder, just remember where you stored it, and hit the save ok. Next in your email that you are composing click on the attachments button at the top of the email, when that dialog box opens browse to the place where you stored your saved image, click that image name to select it then click to save or open or what ever it says there at the bottom and then you should see where it has added that location address to your email in the attachments area. To see if it is working I suggest you try it by sending an email to your own email address and see how it works.

You have to save the image to your pc fist you can not send it directly from a webpage.

Is the image on a web page? You could try to right-click the image and if there is an option to Save Image As, you could save it to your computer. It would probably be saved in Documents (or My Documents) unless you selected a different location. You could then insert the image in an email or attach it to an email. Be advised that an image from a web page is often low-resolution and may not look as good in your email as it does on a web page.

Many times you can right click on a picture on the internet and choose 'save image as' from the context menu. If I want one where right click doesn't work I use a screen capture utility called PicPick.
How you put the image in your email depends on what email you're using. Tell us and someone will help.