Example sentences
tā他shì是wǒ我de的hǎo好péng朋yǒu友。
He's my good friend.
péng朋yǒu友lái来le了。
A friend has come.
About this word
朋 and 友 both mean "friend", so the compound doubles the same idea, the way 工作 doubles "work". Chinese does this often: when both characters carry one meaning, the pair delivers that meaning and adds weight rather than a new sense. 友 is the more productive half, showing up in 友好 (friendly) and 网友 (online friend). Note the pronunciation, since 友 goes neutral: péngyou. That loss of tone is a common sign a compound has settled into a single word. The trap is 女朋友 and 男朋友, which mean girlfriend and boyfriend. For a friend who happens to be female, say 女性朋友, or you are announcing a romance.
The story behind the character
朋
The earliest 朋 is two strings of cowrie shells hanging together. Shells were money, so 朋 was a unit of currency. Ten shells made one 朋. "Friends" were people who studied and spent money together. Your 朋友, at the literal root, is two strings of cash.
友
Two 又 (hands), joined together. Xu Shen wrote 友, 同志为友: "those who share a purpose are friends." Two people holding hands. That's friendship, so simple it needs no explaining.