There are couple ways to attach files to a well and they are both very straight forward.

By way of file selection...

1. On the well edit page, scroll to the Attachments panel
2. Click the Select file button...  (see attachment called Region1.png)
3. ... and browse to the file in question.  When you select the file it should show in the File name: box, then click the Open button.  The Open button may have a different name depending on which browser you are using.  (see attachment called Region2.png)

The file should automatically upload at this point.
By way of drag-and-drop...

1. With the well edit page open and scroll to the Attachments panel
2. Open a file browser (such as Windows "Explorer") and find the file you wish to upload.
3. In your file browser if you click and hold your mouse button on the file in question,  you can drop it on the or drop file here text next to the next to the Select file button...
4. An outlined area should show on the page roughly where the Select file button is.  Just drop the file anywhere in that outlined area that says or drop file here.  (see the attachment called Region3.png)

Again, the file should upload automatically.