Need help with adding code for sequential numbering on an invoice template

Hi

I have been given a task of setting up an Excel 2010 based quote template. I have done most of it, but I could really use some help in sourcing code for sequential numbering. I need the template to generate a new number each time it is opened. I also need to be able to save completed quotes and keep the number that it was given on the quote. I have not used macro's before, so I have little idea of where to begin. Your help is greatly appreciated.

Thanks for that. when I ran the macro it brought up a new number (5). Can you tell me how I can apply this macro to my workbook? Is it only linked to it's current workbook?

Unfortunately I'm unable to upload it because it is on the work server and we are prevented from doing this. Thankyou very much for your help anyway.