in chinese culture, “天” and "地“ are the biggest things. ”天子“ the son of Heaven, the emperor; “地” the people, the animals on the earth. so if a person "天不怕，地不怕", it means this person is not afraid of anything.

Literally, it means "he is not afraid of the sky, nor the earth". However, in Chinese, it means that he's not afraid of heavenly retribution, or the judgement of any gods, and he's also not afraid of earthly retribution, for example laws, or people's hatred, etc. In essence, it means someone is not afraid of spiritual punishment, or physical punishment. It means that he isn't afraid of anything, but it has a sort of negative connotation. If you're trying to say "brave" as in for a hero, it might be better not to use this phrase. It conveys a kind of reckless behaviour, or something akin to provoking authority. It might also be used admiringly, perhaps by young kids looking up to their seniors for being bold.

儒家文化中 有 " 天地君親師 " 為至尊的倫常觀念 也是人應感恩的對象 天地居首 地位尊崇 君親師居於天地之間 天地既已無畏懼 何懼君親師 遑論君親師以外之物? 這個 "天地" 的背後 還有哲學思想存在 不是 眼睛所見的 sky 和 ground 的表象而已

Here 天 is sky, 地 is earth or ground.

天地 means the universe. Traditional Chinese believe that 天 is the laws of physics with conscious, there are god somewhere to control the natural phenomenon and the disasters appeared because the god is angry. And 地 breed all living creatures.