Basic question: how do I inset an image?

[#1]

There is an image button in the icons, but I cannot work out how to use it.
What so you you need to start off with?  a.jpg file?  a .pdf file?
I specifically want to post some screen dumps (produced by pressing [print screen] and pasting into Excel.  I have also printed to a .pdf file, but none will seem to go in and display.
I'm sorry its so basic, and there may be instructions somewhere, but could somebody help, please? ..

[#2]

What would go between [img]...[/img] tags would be the location of an image file (eg .jpg or .png) somewhere on the internet so browsers could fetch and display it.
However rather than using this tag I think you need to attach your image file(s) or PDFs to a post. You do that by clicking Additional Options and Attachments when writing a post, and use the Attach/Browse text box to locate the file to be attached on your computer (file types .jpeg, .jpg, . png and .pdf are allowed). Then when you Post the reply your file(s) will be uploaded and displayed with your post.

[#3]

a simple rule,
if the file is on your computor, you have to use attach
if it is on the web you have the choice, the attach or the img button

[#4]

Thank you Gentlemen
All is now clear!