call at a place

visit for a short time

They called at your office, but did not get past the girl at the front desk.

The man's dead body had been found when police called at his house to interview him about a serious crime.

call for smth

require, demand

The subject here is often an impersonal word or phrase such as:

the situation/this sort of work/this etc.

The object is then usually some quality:

e.g. courage/patience/a steady hand etc.

But it can also be used with a personal subject

The situation called for desperate measures.

Congratulations, David! You're a grandfather! This calls for a celebration!

There is one thing I learned from my grandmother; it's that weaving calls for patience.

The recipe called for brown sugar and sherry, which I knew for certain my grandmother did not have.

call in

stop somewhere on the way to somewhere else (has the same meaning as look in and the colloquial drop in)

Call in on your way home and get a rundown of the day's events.

Sam called in to pick up his newspaper before he went to the doctor's office.

call in smb

summon, send for smb/ask smb to come to the house to perform some service, send for is more authoritative than call in which is therefore a more polite form

I called in a crew to plaster the ceilings and scrape off Mother's old wallpaper.

The Jones called in another plumber to evaluate the situation with the sewage.

call on/upon smb

ask somebody to do something/ask somebody to help (usually + infinitive)

This is a rather formal way of making a request and is chiefly used on formal occasions or in speeches etc. There is usually the idea that the person called upon will consider it his duty to comply with the request

I phoned hundreds of random numbers and called on people to vote for James Baker, because he is the man of the future.

More than once, President has called on him as a trusted adviser in foreign policy matters.

call off smth

cancel something not yet started, or abandon something already in progress

No one knew why Emily had called off (=cancelled) the wedding.

By 10:00 p.m. on Christmas eve, the search is called off for the night.

call out smb

summon someone to leave his house to deal with a situation outside. It is often used of troops when they are required to leave their barracks to deal with civil disturbances 

The President, I think very mistakenly, called out the troops to ban the demonstration.

The governor declared a state of emergency and called out the National Guard to help clear roads.

call up smb

(a) summon for military service 

Olga's brother Boris, 18, recently flunked his college entrance exams, meaning that in the next few weeks he will be called up for duty in the military.

call up smb

(b) telephone 

When the police called up her father the first time, he hung up on them.

Bob called up a particular restaurant with a particularly great view, and requested a particular table.