地【de】

地 turns a description into a manner adverb. It goes between the description and the verb.

The character is read de here, not dì. Same sound as 的 and 得, different job.

Which 地 and which 得

地 comes before the verb and says how the action is carried out. 得 comes after it and rates how it turned out.

The English is the same; the Chinese is not. 认真地写 describes the intention going in, 写得很认真 the result coming out. When the sentence is about how well something was done, 得 is the one you want.

One-syllable adjectives usually skip it

快走, 多说, 少吃 – no 地. The two-syllable and doubled forms take it: 慢慢地走, 认真地看.

It is often dropped in speech

慢慢说 and 慢慢地说 are both fine. Writing keeps 地 more often than conversation does.

Not every adverb takes 地

很, 都, 也, 就, 还, 已经 attach straight to the verb. Yě也de地qù去 is wrong. 地 belongs with descriptions, not with the small adverbs.