You may have things a bit backwards here. First thing's first:
How you create an email signature block is going to depend on what email client you are using at work. Most of them allow you to attach an HTML file as a signature block with an embedded image but you should check your email program's help files first.
As for the image, you simply need to right click on the image and select "Save Image As" or something similar and then chose a spot on your computer to put it. Or, since this is going to be used by everyone at your company, you'll probably want to put it out on your shared network drive somewhere and then have IT lock the file so nobody else can delete it.
To create your signature block, usually you just want to open a text editor such as Notepad and write your code in there. Then save the file as an HTML file by choosing "All files" under the Save As Type block and then append .html to the filename. Here's an example signature block (with image embedded like you would when using Thunderbird):
Hope that helps.
<img moz-do-not-send="false" src="file:///C:/image.gif" alt="Signature">
<br>Daydreamer in Chief
<br>Web: <a href='http://www.htmlhelpcentral.com/'>HTML Help Central</a>
<br>Email: <a href='mailto:email@example.com'>firstname.lastname@example.org</a>
<br>Phone: (800) 555-1212