It shall have two shoulder-pieces attached is literally “two shoulders joined there shall be to it.” From the description that follows, Good News Translation‘s “shoulder straps” seems to be a better translation.

To its two edges, that it may be joined together is rather difficult to understand. Literally the Hebrew says “unto two of its ends and it is joined.” Hebrew Old Testament Text Project recommends a different reading, “on its two ends it shall be joined.” But this does not help to clarify just what the ephod looked like.

It is necessary first to decide whether it was worn above or below the waist, and whether it was worn in front or in back. Then one must decide whether its two edges refers to “the sides” (Good News Translation), “its two upper ends” (New American Bible), “its corners” (New International Version), or “at the front and at the back” (Translator’s Old Testament). Probably it was a kind of apron that covered both front and back from the waist down, and the “shoulder straps” were like suspenders, attached either “to the sides” (Good News Translation) or “at the front and at the back” (Translator’s Old Testament).

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .