Jiǎ rú (假如) and jiǎ shǐ (假使) both function as connectors in the main clause in forming a conditional adverbial clause indicating a hypothetical situation. Jiǎ shǐ (假使) is commonly used in formal or ancient Chinese, jiǎ rú (假如) as its variant, is used more in modern Chinese. They both translate to “if” in English.
jiǎ rú /jiǎ shǐ nǐ zài lù shàng jiǎn dào le yí gè qián bāo, nǐ huì zěn me chù lǐ ne?
what would you do if you found a wallet on the road?