Welcome
The .acsm file is a ticket that tells Adobe Digital Editions where to download the book and what kind of license to give it (or something like that). You need ADE installed on your computer and then open the .acsm with it and the actual book (ePub or PDF) will download. However the book will have DRM which would need to be removed before it could be converted for Kindle.
Just so you know Amazon and Overdrive have announced that library books will be available for the Kindle sometime this year (your libraries current collection will be made Kindle compaitble in some way).