Can 表示你会做某件事（能力），或者某件事是可能的：I can swim = 我会游泳。We can start now = 现在可以开始了。我们也用 Can you...? / Can I...? 来请人帮忙或请求许可：Can you help me?Can I sit here?
can 表示什么
I can ride a bike. = I know how to ride a bike.
It's sunny, so we can play outside. = it's possible.
Can you open the door? = asking for help.
Not "I can swim. = I want to swim." — say "I can swim. = I know how to swim.". Can 说的是能力或可能性，不是想不想。
试一试: Marisol says, "I can cook." What does she mean? (She knows how to cook. / She wants to cook. / She must cook.) 答案: She knows how to cook. — Can 表示能力或可能性。"I can cook" 的意思是她会做这件事——不是她想做，也不是她必须做。
试一试: You need help. Which sentence asks someone for help? (Can you help me? / I can help you. / You can help.) 答案: Can you help me? — 我们用 Can you...? 来请别人帮忙。"Can you help me?" 是一个请求。其他几句只是说某人有能力帮忙。
can + 动词原形
造 can 的句子，用 can + 动词原形。不加 to，不加 -ing。
I can swim.
She can drive.
They can help you.
Not "I can to swim." — say "I can swim.". can 和动词之间什么都不加，没有 to。
试一试: Diego ___ at Farrisen Gym. (can swim / can to swim / can swimming) 答案: can swim — can 后面直接用动词原形：can swim。can 后面不加 "to"，也不加 "-ing"。
所有人都一样（不加 -s）
Can 永远不变。He、she、it 也用 can，不加 -s。
I can cook.
She can cook.
They can cook.
Not "She cans cook." — say "She can cook.". 即使用 she，也还是 can，绝不是 cans。
试一试: Camila ___ really well. (can cook / cans cook / can cooks) 答案: can cook — can 从不加 -s，它后面的动词也保持原形：Camila can cook（不是 "cans" 或 "cooks"）。
否定：can't
表示 不能 时，用 can't + 动词原形。完整形式是 cannot（一个词）。
I can't swim.
He can't drive.
We cannot come today. = We can't come today.
Not "I don't can swim." — say "I can't swim.". can 的否定式是 can't，不是 'don't can'。
试一试: Sorry, I ___ today. (can't come / don't can come / can't to come) 答案: can't come — can 的否定式是 can't，后面接动词原形：I can't come（不是 "don't can"，也不加 "to"）。
疑问句：Can 放最前
要提问，就把 Can 放在那个人前面，后面接动词原形。
Can you swim?
Can she drive?
What can I do?
Not "Do you can swim?" — say "Can you swim?". 问句里 Can 放最前面，不需要 'do'。
试一试: ___ you help me with this? (Can / Do can / Are) 答案: Can — 用 Can 开头，放在那个人前面：Can you help me? can 前面不用加“do”。
试一试: Remember what follows can, Lani ___ a bike. (can ride / can rides / can to ride) 答案: can ride — can 后面永远是动词原形：can ride。（不加 -s，不加 "to"，不加 "-ing"，每次都一样。）