Algorithm question what does this mean
 

hi everyone
im my computer science degree am doing a module on algorithms

tho we are studying it i am bit behind

my question is
what does n - 1 mean (n minus 1)

what does n/2 mean (n over 2 or n divided by 2)

because stuff like this is being mentioned am soo confused when the being used i need to know what they mean, and why is it being used and when would you use them..

please can anyone help