Build both the same way: used to or would + the base verb (the plain form: go, walk, live). used to and would already carry the past, so the verb after them never changes — say used to go and would go, never used to went or would went.
How to build it
We used to go to the lake. (base verb: go, not went)
She would call every Sunday. (base verb: call)
He used to walk to work. (base verb: walk)
Try it: Every day, we ___ home together. Which is right? (used to walk / used to walked / would walked) Answer: used to walk — After used to and would you always use the base verb (walk), never the past form (walked). Used to and would already show it happened in the past.
Repeated actions: both work
For a repeated action in the past (something you did again and again), you can use used to or would. They both work, and they mean the same here.
Every summer, we used to go to the lake. / Every summer, we would go to the lake.
She used to call every Sunday. / She would call every Sunday.
He used to walk to work. / He would walk to work.
Try it: As a child, every winter I ___ build a snowman. Which is right? (used to (or would) / am used to / use to) Answer: used to (or would) — Building a snowman is a repeated action, so both used to and would work here. "Am used to" means accustomed (a different idea), and "use to" is missing the -d for the past.
States: only used to
For a state (something that just was, not an action you did, like live, be, have, like), only used to works. would can't be used for a state.
I used to live in Paris. (a state, not "I would live")
She used to be shy. (a state)
We used to have a dog. (a state)
Not "I would live in Paris." — say "I used to live in Paris.". Living somewhere is a state, so use used to, not would.
Try it: Before she moved, Mei ___ a small flat near the harbour. (used to have / would have / would had) Answer: used to have — Having a flat is a state, not a repeated action, so only used to works: used to have. "Would" for past habits only fits repeated actions, never states like have, be, or live, so it can't be used here, and "would had" mixes up the words.
Negative and question: use did
For the negative and the question, bring in did: didn't use to + base verb, and Did … use to + base verb? Watch the spelling — after did/didn't, drop the -d: write use to, not used to.
Negative: I didn't use to like coffee. (not didn't used to)
Question: Did you use to live here? (not Did you used to)
We didn't use to have a car.
Not "I didn't used to like coffee." — say "I didn't use to like coffee.". After did/didn't, drop the -d: it's use to, not used to.
Try it: Complete the negative: When I was young, I ___ vegetables. (didn't use to like / didn't used to like / wasn't use to like) Answer: didn't use to like — The negative is didn't use to + base verb. After didn't, drop the -d, so it's "use to," not "used to." "Wasn't use to" mixes up the past-habit form with be.
Try it: Make it a question: ___ a bike to school? (Did you use to ride / Did you used to ride / Do you used to ride) Answer: Did you use to ride — Questions use Did + subject + use to + base verb: Did you use to ride? After did, drop the -d (use to, not "used to"), and use Did, not Do, because it's a past habit.
Try it: One is a state, the other a repeated action. Which sentence is right? (He used to be shy, but he would always say hello to everyone. / He would be shy, but he used to always say hello to everyone. / He would be shy, but he would always say hello to everyone.) Answer: He used to be shy, but he would always say hello to everyone. — "Be shy" is a state, so it needs used to. "Say hello to everyone" is a repeated action, so would (or used to) works. The state takes used to; the repeated action can take would.