想讀law, 但不知從何入手??

I assume you want to pursue a legal career in Hong Kong. I recommend that you do all your legal studies in HK since the practicing requirements for foreign law graduates have been tightened in HK (you have to do conversion exams which have low passing rates)

LLB= bachelor of laws
LLB is basically a university degree in law. It takes 4 years to complete LLB in Hong Kong. However, this solution probably will not be available to you. HKU used to provide LLB fast track programme (3 years) for graduates in other disciplines, but it will stop doing so next year.

The way forward, I think, is to take Juris Doctor (JD). It is offered by both CUHK and CityU and HKU will offer it next year to replace its LLB fast track programme. JD only takes 2 years to complete (but includes summer semesters~you don't get summer holidays). After JD you need to study PCLL and then become a trainee (2 years with pay, solicitor)/pupil (1 year without pay, barrister) to become a qualified lawyer.

PCLL= Postgraduate Certificate in Laws
PCLL is a must if you want to become a lawyer. It is the professional qualification for lawyers in HK. Without PCLL you cannot become a trainee/pupil and cannot practise.
As said by its name, PCLL is only offered to law postgraduates. If you successfully complete LLB or JD and your grades are decent, you will get admitted to PCLL. The course takes a year to complete.

CPE=Common Professional Exam
The Common Professional Examination (CPE) is a postgraduate law course in England Wales that is taken by non-law graduates (graduates who have a degree in a discipline that is not law or not a qualifying law degree for legal practice) wishing to become a lawyer in the UK.The course thus allows non-law students to convert to law afteruniversity. For full time CPE, a year is needed to complete the course. However, as said, if you want to practice in HK, studying in HK for a JD would be a better choice due to various conversion exams required.