gcse sciences help

ive been getting 8/9s in sciences from as far as i remember but one thing i struggle with most with science is exam questions. everytime there is a 2,3,4,5,6 marker ill always get only half of the marks or even 0 sometimes and its not even because i dont know the content, i jsut dont understand whatll please aqa into giving me the marks bc ill look at the mark scheme dumbfounded about how they even got half the points on there pls give me some tips tyy ^^