What is the difference between 朋 and 友?
If 朋友 means friend then why does the characters 朋 and 友 also mean friend separately and how do you tell when to use one or the other?

Question

Answer

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.

Answer

朋友is the most commonly used word  eg：你是我的朋友。 我们是朋友。
朋&友is writings in classical style.also be used in modern Chinese 
eg：有朋自远方来！A friend is coming from far away!【classical 】
       朋党 clique;cabal【modern Chinese】
eg：妇女之友 the friend of mowen（magazine‘s name）【classical &modern Chinese】
       友于 brother【classical】
       友军 friendly forces【modern Chinese】
       友人 friend【modern Chinese】
       友谊 friendship;amity【modern Chinese】
       友邦 friendly state【modern Chinese】
       友爱 friendly affection;fraternal love【modern Chinese】

Answer

You don't use them separately. 朋 and 友 are two characters that are not used separately, only in conjunction with others.

Answer

朋和友的意思是一样的，一般如果表示friend的话，就直接用“朋友”就可以了。在中文中，有很多词语的语义是重复的，不必过分纠结。

Answer

these are two parts of one word
and
these parts can be connected with other symbols to make new words
however
neither of them doesn't mean "friend" separately
for example you cannot say "他  是  我的  朋"