Exodus 28:4 lists the garments (ephod, breastpiece) that require the stones mentioned here.

Exodus 28:9-21 details how the onyx stones are set into the ephod and breastpiece.

Exodus 28:15 describes the breastpiece, one of the items for which stones are designated here.

In Exodus 39:6, the onyx stones are set into the ephod, directly fulfilling the instruction for stones in the earlier verse.