Japanese count by holding their hand open and closing their fingers one by one starting with their thumb.
この場合、次のような言い方ができますよ。
ーJapanese count by holding their hand open and closing their fingers one by one starting with their thumb.
「日本人は手を開いて、親指から一本ずつ指を閉じて数を数えます」
to count「数える」
to close one's fingers「指を閉じる・指を折り曲げる」
one by one「一つずつ」
thumb「親指」
ご参考まで！
カナダ 
