To say that you are doing something before or after another thing, put 以前 (yǐqián, before) or 以后 (yǐhòu, after) after the action.
我们吃饭以前要洗手。
Wǒmen chīfàn yǐqián yào xíshǒu.
Before eating, we have to wash (our) hands.
我们下班以后一起看电影吧！
Wǒmen xiàbān yǐhòu yìqǐ kàn diànyǐng ba!
After we get off work, let's watch a movie together!
看了电影以后，我们去喝啤酒吧！
Kàn le diànyǐng yǐhòu, wǒmen qù hē píjiǔ bā!
After watching the movie, let us go drink beers!
You can also use 以前 as an adjective to say previous!
这是他以前的女朋友。
Zhè shì tā yǐqián de nǚ péngyǒu.
This is his previous girlfriend.
To say that you are doing something immediately, add 马上 (mǎshàng, immediately) before the action.
你要马上睡觉！
Nǐ yào mǎshàng shuìjiào!
You have to sleep immediately!
我想马上见你！
Wǒ xiǎng mǎshàng jiàn nǐ!
I want to see you immediately!
吃饭以后，一定要马上刷牙。
Chīfàn yǐhòu, yīdìng yào mǎshàng shuāyá.
After eating meals, (you) definitely have to immediately brush (your) teeth.
To talk about doing two things at the same time, put 一边 (yìbiān, at the same time) before each of the two actions.
我喜欢一边洗澡，一边唱歌。
Wǒ xǐhuān yìbiān xǐzǎo, yìbiān chànggē.
I like to sing and shower at the same time.
她一边跑步，一边听音乐。
Tā yìbiān pǎobù, yìbiān tīng yīnyuè.
She runs and listens to music at the same time.
我爸爸一边刷牙，一边跳舞。
Wǒ bàba yìbiān shuāyá, yìbiān tiàowǔ.
My father brushes teeth and dances at the same time.
还 (hái, still) means still. To say that you still haven’t done something, you can add 没有 (méiyǒu, haven't) after 还 (hái, still).
我还没有洗澡。
Wǒ hái méiyǒu xǐzǎo.
I still haven’t showered.
他们还没有起床。
Tāmen hái méiyǒu qǐchuáng.
They still haven’t gotten up.
她还没有刷牙。
Tā hái méiyǒu shuāyá.
She still hasn’t brushed (her) teeth.