That cake shop is using their success at their actual store as a stepping stone and have began selling their goods online as well.
ご質問ありがとうございます。
"That cake shop is using their success at their actual store as a stepping stone"＝「あのケーキやは、実店舗での成功を足掛けにしている」
"and have began selling their goods online as well."＝「そして商品をネットでも売り始めた。」
ご参考までに。
アメリカ合衆国 
