Help me please I CANT STUDY MY EXAMS ARE BEHIND THE DOORS?

Many times when i solve IGCSE CAMBRIDGE biology questions. I pick up the mark scheme to check out the answers but, i am always don't know what to do? (e.g if the question carry 3 marks and they wrote an answer followed by a seperating poitt(;). How they write for example 7 points and they didn't write ANY 2 OR 3 1 MARK EACH so how do i know how many point to wrrite and how it will be marked. Especially in planning experiments the ques carry e.g six marks in m.s they write 13 point what do i do,-NO HALF A MARK IN THE IGCSE- if i didn't write one point so one mark minus or WHAT? I fed up really i always shuffle the pages and then swear on the examiner(LOL) HELP ME IT SUCKS