Upload File Using Form

I am trying to upload a CSV file through a form, process it, then input the values in the file it into my database. So first step, I need to upload the file. I created the form, uploaded a test file but I am having trouble accessing the file in my controller. I can access a hash but all contains is the original filename of the file. I guess my question is how can I access this file and save it so that I can later pass it to a CSV processing function. I assume the file is uploaded to some sort of temp file? I am new at rails but I have accomplished uploading and saving files in PHP before. Any help would be great.

Thanks,

Jason