1. make friends: to start to be
someone's friend, especially when you have to make an effort to do this
例：
Her family moved a lot, and it wasn't
always easy to make friends.（她老搬家，一直很难交上朋友。）
The children soon made friends with the
kids next door.（孩子们很快和邻居小孩交上了朋友。）
2. hit it off: if two people hit it
off, they immediately become friends when they meet for the first time
备注：''hit it
off''是较口语化的用法。
例：
I knew you and Mark would hit it off.（我就知道你和马克会一拍即合。）
The two men ended up in the same business
law class and hit it off immediately.（这两个人最后上了同一个商务法课程，并且马上交上了朋友。）
Though we work together, we've never really
hit it off.（我们虽然是同事，但是我们不算是朋友。）
3. click: if two people click, they
like each other immediately when they first meet, because they have the same
ideas or opinions, or laugh at the same things
备注：''click''是较口语化的用法。
例：
They met at a party and clicked right away.（他们在一个派对上认识的，一拍即合。）
We just clicked, and we've been friends
ever since.（我们一拍即合，从那时起就交上了朋友。）
I know him fairly well, but we've never
really clicked.（我跟他很熟，但是我们算不上真正的朋友。）
I never really clicked with my boss, and it
made work a little more difficult.（我跟老板一直不怎么合拍，这给工作带来了一点麻烦。）
4. strike up a friendship: to make
friends with someone very quickly, especially if you do it intentionally
备注：''strike
up''原意是''to begin
something''，如''I struck
up a conversation with him at the party.''（在派对上我找他聊了会天）。同样，''strike up''后面加上''a friendship''就表示“开始交朋友”。
例：
The two women struck up a friendship when
they met on holiday.（这两位女士度假时遇到，交上了朋友。）
We met for the first time at a business
conference, and we immediately struck up a friendship which has lasted for
years.（我们初次见面是在一个商务会议上，我们马上交上了朋友，这份友谊持续了好多年。）
5. befriend: to be friendly to
someone who needs help, for example someone with financial or emotional
problems
例：
His parents befriended some American
soldiers who served in Wales during World War II.（二战期间，他的父母跟一些在威尔士服役的美军士兵交上了朋友。）
It's fairly unusual for high school seniors
to befriend freshmen.（在高中里面，高年级生和新生交朋友并不常见。）
He befriended the new student.（他跟这个新生交上了朋友。）
6. fall in with: to begin to be friends
with a group of people, especially people that other people do not approve of
备注：在口语中常作''get
in with''。
例：
He's fallen in with a group of boys I don't
like very much.（他跟一伙我很不喜欢的孩子混在一起。）
She used her husband's money and family to
get in with a group of Hollywood's social elites.（她利用夫家的财力和影响力，跟一群好莱坞的名人搭上了。）
Her daughter fell in with a bad crowd.（她女儿跟一群坏人混在一起。）