To move files into folders, click on the ellipsis opposite the relevant file then click the "Move" button. On the opening pop-up choose the folder in which you want to move the file.

To move multiple files at the same time, first, check the boxes on the left side of the relevant files, then click on the "Move" button in the upper right corner. Then on the opening pop-up choose the folder in which you want to move the file.