Compare in and out:
in = into a room, a building, a car, etc.
– How did the thieves get in?
– Here’s a key, so you can let yourself in.
– Sally walked up to the edge of the pool and dived in. (= into the water)
– I’ve got a new apartment. I’m moving in on Friday.
– As soon as I got to the airport, I checked in.
In the same way, you can say go in, come in, walk in, break in, etc.
Compare in and into:
– I’m moving in next week.
– I’m moving into my new apartment on Friday.
out = out of a room, a building, a car, etc.
– He just stoop up and walked out.
– I had no key, so I was locked out.
– She swam up and down the pool, and then climbed out.
– Tim opened the window and looked out.
– (at a hotel) What time do we have to check out?
In the same way you can say go out, get out, move out, let somebody out, etc.
Other verbs + in
drop in = visit somebody for a short time
– I dropped in to see Chris on my way home.
join in = take part in an activity that is already going on
– We’re playing a game. Why don’t you join in?
plug in an electrical machine = connect it to the electricity supply
– The fridge isn’t working because you haven’t plugged it in.
hand in / turn in homework, a report, a resignation, etc. = gave something written to a teacher, boss, etc.
– Your report is due this week. Please hand it in by Friday at 3 p.m.
fit in = feel you belong or are accepted by a group
– Some children have trouble fitting in at a new school.
Other verbs + out
eat out = eat at a restaurant, not at home
– There wasn’t anything to eat at home, so we decided to eat out.
drop out of college / school / a course / a race = stop before you have completely finished a course / race, etc.
– Gary went to college but dropped out after a year.
get out of something that you arranged to do = avoid doing it
– I promised I’d go to the wedding. I don’t want to go, but I can’t get out of it now.
cut something out (of a newspaper, etc.)
– There was a beautiful picture in the magazine, so I cut it out and kept it.
leave something out = omit it, not include it
– In the sentence “She said that she was sick,” you can leave out the word “that.”
fill out a form, a questionnaire, etc = write the necessary information on a form
– I have to fill out this application by the end of the week.