A premium transfer is when a file is downloaded using the data cap on your subscription plan. These can be files you downloaded from other people, or other people downloading your files if you have bandwidth sharing enabled. Bandwidth sharing can be changed on the subscription page.
Total bandwidth usage is the combined bandwidth usage of all the files on your account. This includes paid transfers.
A view is counted when someone visits the download page of one of your files. Views are unique per user per file.
Downloads are counted when a user clicks the download button on one of your files. It does not matter whether the download is completed or not, only the start of the download is counted.