What is the difference between Usul al-Fiqh and the science of Fiqh, and what is meant by detailed and practical evidences?

The difference between Fiqh and Usul al-Fiqh: Fiqh specializes in clarifying practical Sharia rulings derived from their detailed proofs, such as a faqih's statement: "Prayer is obligatory," based on the Almighty's saying: {And establish prayer}. As for Usul al-Fiqh, it is a science that investigates the general proofs of Fiqh, how to benefit from them, and the condition of the one benefiting. What is meant by general proofs are the overarching rules, such as "a command denotes obligation." And by "how to benefit from them" is meant knowing how to derive rulings from the proofs by studying the rules of linguistic expressions and their connotations. And by "the condition of the one benefiting" is meant knowing the mujtahid and the conditions for his ijtihad.