Islamic Finance: Sources of Shariah

Based on my understanding, there are four sources of shariah:

1. Al Quran
2. Hadith of Prophet Muhammad (pbuh)
3. Ijma (Consensus of Mujtahid)
4. Qiyas (Analogical Reasoning)

Fiqh is human understanding or knowledge of shariah pertaining to human conduct derived from the sources of shariah.

Usul Al Fiqh known as principles of Islamic Jurisprudence which scholars used to derive the fiqh from the source of shariah. For example Ijma (Concensus) and Qiyas (Analogical Reasoning).

My analogies, a designer of hijab. She knows the material, colour, printed material and the design of hijub demanded by customers. She also provided the tutorial of how to wear hijub that looks fahsionable. This must be refer to Usul Al Fiqh. 

At the end, the complete wearing of hijub that satisfy the customers, this is refer to Fiqh.

As far as I know that Usul literally means the roots, it deals with the methods and one of part in the sciences of fiqh.