手 and 指: hands and specific digits
Distinguish the hand used as a means from a particular finger, and use context to interpret 指.
Actions using the hands
手, read て, means hand. 両手で箱を持ちました。 says that someone held a box with both hands. The box is the object, and both hands are the means.
手を洗ってから食べます。 says that someone will eat after washing their hands. てから gives the order; do not reverse it into washing after eating.
Pointing with a finger
指, read ゆび, can refer to a finger or toe. 指で地図の場所を示しました。 describes pointing to a location on a map with a finger.
人差し指 is the index finger. 人差し指でボタンを押しました。 says that someone pressed a button with that finger; do not generalize it into using the whole hand.
Fingers and toes
足の指 means toes. Do not automatically interpret 指 as fingers when 足の specifies the foot.
右手の指に指輪をはめました。 says that someone put a ring on a finger of their right hand. It does not identify which finger, so do not add the ring finger.
Does 右手の指に指輪をはめました identify the ring finger?
Show the answer and why
No. It identifies a finger of the right hand without specifying which one.