If you want to learn how to implement use of NeatUpload I suggest study the source code for existing features that have file upload, such as the Shared Files feature. Note however that NeatUpload only works in Full Trust hosting, by default we have things pre-configured for Medium Trust which is more common. In Full Trust you could use the web.fulltrust.config file by renaming the Web.config to web.mediumtrust.config and renaming web.fulltrust.config to web.config and restore any customizations such as machine key.
So with NeatUpload disabled it falls back to the normal file upload provided in ASP.NET.
I would also recommend be careful about letting strangers upload files and where you put the files and what kinds of files you allow to be uploaded. It is a security concern and one should be very careful about allowing file uploads.
Hope that helps,
Joe