Use am / is / are used to when something is normal and familiar for you now. It doesn't surprise you anymore.
be used to: it feels normal now
I'm used to the cold weather here now.
She's used to working late, so she doesn't mind.
We're used to the noise from the street.
Try it: Hiroshi has lived by the train line for years. He ___ the noise. (is used to / used to / is using to) Answer: is used to — The noise is normal for him now, so use is used to. "Used to" on its own (no is) means a past habit that stopped, which is the opposite of what's happening here, and "is using to" is not a real form.
+ a thing, or the -ing form
After used to here, put a thing (a noun) or the -ing form of a verb, never the base verb.
I'm used to the weather. (a thing)
I'm used to getting up early. (the -ing form)
She's used to hard work and working weekends.
Not "I'm used to get up early." — say "I'm used to getting up early.". After this used to, use the -ing form (getting), not the base verb (get).
Try it: She's a nurse, so she's used to ___ at night. (working / work / be working) Answer: working — After be used to, use a thing or the -ing form, so working fits: she's used to working. The base verb "work" and "be working" don't follow this used to.
get used to: still getting there
Use get used to when you are still adjusting, becoming familiar with something new. The same words follow: a thing or the -ing form.
I'm getting used to the new job. (still adjusting)
She's slowly getting used to living alone.
You'll get used to the early starts soon.
Try it: Mei just moved here. It's strange at first, but she's slowly ___ the quiet. (getting used to / used to / got use to) Answer: getting used to — She's still adjusting, in the middle of it, so use getting used to. "Used to" alone would mean a finished past habit, and "got use to" is missing the -d and the right wording (it's get/getting used to).
used to: true before, not now
Use used to + the base verb for something that was true or a habit in the past but isn't now. There is no be in front of it, and the verb stays in its base form (live, smoke), not the -ing form.
I used to live in Osaka, but now I'm here. (true before, not now)
She used to smoke, but she stopped last year.
We used to walk to school every day.
Not "I use to live in Osaka." — say "I used to live in Osaka.". Keep the -d: it's used to + base verb (live), telling us it was true in the past but stopped.
Try it: Ken doesn't play tennis anymore, but he ___ every weekend when he was younger. (used to play / is used to playing / used to playing) Answer: used to play — It was his habit in the past but it stopped, so use used to + the base verb: used to play. "Is used to playing" means it feels normal now (the opposite), and "used to playing" wrongly adds -ing after past-habit used to, which takes the base verb.
Saying no, and asking
To make these negative or a question, change the small verb, not "used to". For be used to, say I'm not used to it and Are you used to it? For get used to, say I can't get used to it and Did you get used to it? With past-habit used to, the -d drops in the negative and question: I didn't use to like it and Did you use to play?
I'm not used to the cold yet.
Are you used to driving on the left?
I didn't use to like coffee, but now I love it.
Did you use to play football at school?
Three "used to" — tell them apart
Same words, three meanings. Tell them apart by whether there's a be/get and what follows. used to + base verb = a past habit, not now (no be). be used to + a thing or -ing = normal for you now. get used to + a thing or -ing = still adjusting.
I used to smoke. = I don't now. (past habit, base verb)
I'm used to the smoke. = it's normal for me now. (be + thing)
I'm getting used to the smoke. = still adjusting. (get + thing)
Not "I'm used to smoke every day. (meaning the past habit)" — say "I used to smoke every day.". For a past habit, drop the be and use the base verb: used to smoke, not "be used to smoke".
Try it: One part feels normal now; the other you're still getting used to. Which is right? (I'm used to the cold now, but I'm still getting used to the dark mornings. / I'm getting used to the cold now, but I'm still used to the dark mornings. / I'm used to the cold now, but I'm still getting use to the dark mornings.) Answer: I'm used to the cold now, but I'm still getting used to the dark mornings. — Something that feels normal now = be used to: I'm used to the cold. Something you're still adjusting to = get used to: I'm still getting used to the dark mornings. The first part takes be used to; the second takes getting used to.