The vocabulary builder employs an original approach that take into account how many people learn and remember.
What does the word 'employ' mean in 'employs an original approach'? And what's the meaning of this phrase?
It is the definition #2 from this dictionary:
make use of.
Your example reads:
'The vocabulary builder makes use of an original approach that takes into account how many people learn and remember'
Employ can mean use as a tool for accomplishing something.
"Original approach" means what it says - it's a way or path towards something (i.e. approach) that is new or unique (i.e. original).
The vocabulary builder uses an original approach (to teach vocabulary). And, this "original approach" takes into account how many people learn and remember.
We don't know what exactly that approach is.