To ask how cold or how small something is, add 有多 (yǒu duō, how) before the adjective.
明天会有多冷？
Míngtiān huì yǒu duō lěng?
How cold will it be tomorrow?
那双鞋子有多小？
Nà shuāng xiézi yǒu duō xiǎo?
How small are that pair of shoes?
今天有多热？
Jīntiān yǒu duō rè?
How hot is it today?
To say When it rains... in Chinese, you’d say 下雨的时候... (xiàyǔ de shíhou). Notice that 的时候 (de shíhou, when) comes at the end of the phrase!
下雪的时候，这里很漂亮。
Xià xuě de shíhou, zhèlǐ hěn piàoliang.
When it snows, it is beautiful here.
阴天的时候，我喜欢在家看书。
Yīn tiān de shíhou, wǒ xǐhuān zàijiā kànshū.
When it's cloudy, I like reading books at home.
你吃饭的时候，不要唱歌。
Nǐ chīfàn de shíhou, bùyào chànggē.
When you eat, don’t sing.
You’ve learned to use 在 before a verb to show that something is happening right now (e.g., 她在听音乐, tā zài tīng yīnyuè). Another way to talk about something ongoing is to put 着 (zhe, ongoing state or action) right after the verb!
她在等着我们。
Tā zài děng zhe wǒmen.
She is waiting for us.
Notice that with 下雨 (xiàyǔ, rain) and 下雪 (xiàxuě, snow), the main verb is actually 下 (xià, fall), so that’s where you put 着 (zhe)!
外面下着雪，别出去玩。
Wàimiàn xià zhe xuě, bié chūqù wán.
It's snowing outside. Don't go out to play.
外面下着雨，你出去要带伞。
Wàimiàn xià zhe yǔ, nǐ chūqù yào dài sǎn.
It's raining outside. Take an umbrella when you go out.
(Literal: It's raining outside; to go out you need to take an umbrella.)
In English, we can say If you can’t come, you must tell us or If you can’t come, then you must tell us. Either of these works if you’re speaking Chinese in an informal setting, but in more formal settings, you’ll need to use both 如果 (rúguǒ, if) and 就 (jiù, then).
如果你不能来，就一定要告诉我们。
Rúguǒ nǐ bùnéng lái, jiù yídìng yào gàosu wǒmen.
If you cannot come, then you must tell us.
如果明天下雨，我们就不出去。
Rúguǒ míngtiān xià yǔ, wǒmen jiù bù chūqù.
If it rains tomorrow, then we won’t go out.
To say you never do something, simply put 从来不 before the verb.
他从来不喝酒。
Tā cónglái bù hējiǔ.
He never drinks alcohol.
这里从来不下雪。
Zhèlǐ cónglái bú xiàxuě.
It never snows here.
我的猫从来不喝牛奶。
Wǒ de māo cónglái bù hē niúnǎi.
My cat never drinks milk.