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Do you mean you want to get Microsoft Publisher from Office 365?
You can get the latest version of Microsoft Publisher from some of Office 365 Plans, please see this article.
If you have already gotten Microsoft Publisher and just want to know the user guide, please visit this link http://office.microsoft.com/en-us/support/results.aspx?qu=Publisher&ex=2&filter=1&av=zpb.
If you encounter any issue when using Microsoft Publisher, please visit Office Community, you will be directed to the dedicated support after you choose the appropriate product.