Por favor muéstrame oraciones como ejemplos con "Would" and "could" I'm completely confused using these words. . Dime tantas expresiones diarias como sea posible.

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They're the past tense of "will" and "can", respectively.
"He says he will." becomes "He said he would."
"I think he can." becomes "I thought he could."

But they also are used in hypothetical contexts. Consider:

"I will eat."

What if used it in an "if" sentence?

"If I had food, I will eat." ☓

Wrong. "Will" here still means you absolutely will do it, but because it's hypothetical ("If I had food" implies there is no food), we can't use "will". This is where "would" comes in:

"If I had food, I would eat." ◯

It's also used when asking if someone could do something.

"Would you go to the store and get me some milk?"

("Will you go..." sounds quite rude and demanding.)

Similarly, "could" is used as a hypothetical "can". You're saying that you COULD do something, if the conditions were right.

"I can sing."

"I could sing (if I had a microphone/if my throat wasn't sore/if we had some music/but now I'm too old)."

We can also use it in our last "would" example:

"Could you go to the shop and get me some milk?"

Finally, there's a phrase you'll see a lot that uses both.

"I would if I could."

"Ah, shoot, the straps on my shoes broke."
"Just buy some new ones, that pair was getting old."
"I would if I could, but I don't have the money."