We use BY to show HOW we do something

In English we sometimes use the word "BY" to show how we do something.

"Can I pay by credit card?"
(カードで支払えますか。)

"I came here by train today."
(私は今日はここまで電車で来ました。)

"These things are all made by hand."
(この品は皆手細工だ。)

(*We also use the adjective handmade to mean 'made by hand')
These chocolates are handmade.