First of all you need to save the sig' I send you, to your computer. Right click the sig / image and the option to save as a "gif " file should be there. Click to save to your computer, renaming it to whatever name you wish.
Click on Create Mail
Click "Format"
and make sure "Rich Text" (HTML) is selected.
No need to do this part every time.
Click in the main body of the email to get the flashing curser.On the toolbar click "Insert"
and you will see as below
After clicking "Picture" you will see as below. Click on "browse" to find where you have stored the file. Make sure the file is still a .gif file.Press "ok"
Alternately and easier just click icon to the right on the toolbar.Again, make sure you have the flashing cursor in the email body first.