So, there is the artifact (spelled artefact for some reason) system, which is basically reserved for secondary weapons. There are actual weapons, of which can be used to do damage, shields, and vanity offhands. Most of it is explained in this video.
However, to actually make dual wielding useful, in regard to DPS, you need to pick up the corsair class. The sub-weapon cancel skill (of which is mentioned in the video) is used to speed up attacking while dual-wielding. It used to be that this was all manual (shown in the video), but it has recently been nerfed into a buff that just makes you attack faster. There are also skills that require off-hand / artefacts to be equipped in order to be used, such has various shield skills or the rogue’s backstab (which requires you to have a crossbow + off-hand / dagger).