Complex sentence: In 2004, Vans launched the Vans "Customs" feature on its website, whereby customers could log onto the Vans website and design their own pair of Vans Slip-ons, mid-cuts, or high-tops.
Split into simpler sentences: In 2004, Vans launched the Vans "Customs" on its website. This allowed customers to log onto the Vans website and design their own pair of Vans Slip-ons, mid-cuts, or high-tops.