Non-native speakers of Chinese can often get the words 长 (zhǎng) vs 长得 (zhǎngde) mixed up. Both these words are about “growing”, but they have different functions. Let's look at them one by one.

长 (zhǎng): to grow, to develop

The word 长 itself means “to grow” (note that this is pronounced zhǎng, and not cháng). It can mean “to grow” as in to grow larger or to develop physically, or to grow a particular feature. Let's have a look at some example sentences:

她长高了五公分。

Tā zhǎnggāole wǔ gōngfēn.

She's grown five centimetres taller.

草已长了根。

Cǎo yǐ zhǎngle gēn.

The grass has grown roots.

树长叶子了。

Shù zhǎng yèzi le.

The tree has grown leaves.

我长了痘痘。

Wǒ zhǎngle dòudou.

I've got a spot. (lit. I've grown a spot.)

Notice how 长 is about growing or developing features. 长 also combines into varius words related to growth, such as 增长 (zēngzhǎng).

长得 (zhǎngde): present state of growth, to look…

长得 is used to talk about the present state of growth or something, and by extension, how something or someone looks. Adding 得 to 长 is like saying “the result of growth is”: it's how something appears now. Some example sentences:

他长得很帅。

Tā zhǎngde hěn shuài.

He's very handsome.

她长得比较结实。

Tā zhǎngde bǐjiào jiēshi.

She's grown quite strong.

他长得很像他爸爸。

Tā zhǎngde hěn xiàng tā bàba.

He really looks like his dad.

那些树长得太高了。

Nàxiē shù zhǎng de tài gāole.

Those trees have grown too tall.

Notice how 长得 is about the result of growth or an appearance or state that has developed.