朋，月+月，pictographic and associative character, meaning： two ”bodies“ stick together--> too people are always together-----> friends
友，echoism，in oracle， it's like two hands in one direction, meaning: help or cooperation.
both 朋 and 友 has the meaning of friend，but we don't use 朋 separately， 友 is ok tho，eg：
好友--good friend = 好朋友
but you can see such idoms： 亲朋好友 good friends，朋比为奸 act in collusion with
in most cases， when you try to use the word ”friend“， 朋友 is commonly used.
other words related to 朋 or 友 separately， are used in idoms.