If you put the same thing in two or more sel boxes, those tunes will be returned in an arbitrary order. So if you don't care about the order, you can just use 'x' or any other character to select the tunes you want.
When you've selected some tunes, go to any of the lines with a GET button. Make sure that the output formats you want are checked. Then press the GET button to download the tunes.
Note that if you select any of the ABC, TXT, GIF or PNG formats, they will be shown in the resulting web page. Other formats such as PS, PDF or MIDI must be downloaded separately. You'll see a small table of all the resulting files at the bottom, where you can click to get the tunes in these other formats.