地(dì) - ground, earth, land (also the adverbial particle de) in Mandarin

地 does two entirely separate jobs, and they are read differently. Said dì it is a noun meaning ground, earth, land or place: 地上 (dì shàng) is on the ground, 地方 (dìfang) is a place, 土地 (tǔdì) is land or soil, and 地球 (dìqiú) is the Earth itself. Said de, in the neutral tone, it is a grammatical particle with no meaning of its own.

The particle is the half English speakers get wrong. It attaches a description to a verb, turning it into an adverb: 慢慢地走 (mànmàn de zǒu), walk slowly; 高兴地跑 (gāoxìng de pǎo), run happily; 认真地听 (rènzhēn de tīng), listen attentively. The pattern is always description + 地 + verb, and the 地 sits in front of the verb, never after it.

That puts 地 in the middle of Mandarin's classic three-way trap, because 的, 地 and 得 are all read de and all sound identical.

的 (de) links a description to a noun: 漂亮的花 (piàoliang de huā), a pretty flower. 地 (de) links a description to a verb that follows: 慢慢地走 (mànmàn de zǒu), walk slowly. 得 (de) links a verb to a comment on how it was done, and that comment comes after: 走得很慢 (zǒu de hěn màn), walks slowly.

The short test is what sits on either side. Noun on the right means 的. Verb on the right means 地. Verb on the left means 得. Native speakers hear no difference at all, which is exactly why the written distinction is worth drilling.