Hi @Anonymous, welcome to the Autodesk Community.
The pepetual software that you have purchased is available for download from your Autodesk Account at https://accounts.autodesk.com In the "Management" view, you should see AutoCAD LT 2014 listed and you can choose to "Download Now" or "Install Now" from there. The serial number and product key (required for installation) are also available by expanding the view of the AutoCAD LT listing. Physical media, like a CD or DVD, is not required.
If you do not already have an Autodesk Account, or if you log in and cannot find your software, please Contact Us via this link where you can online chat with a Customer Care representative: http://knowledge.autodesk.com/contactus/downloads-upgrades/finding-download
To address your second question about the length of time your license is valid... it is a perpetual license so it does not expire. You can run it for as long as you like, or until you upgrade to the current release.
I hope this helps.
Regards,
Felice
Felice S
Consumption Business Models Team