Do colleges look at your grade for the end of the year or do they look at each grading period?

Yes, colleges will typically look at your end-of-year grades, or the cumulative grade for each course, if you have a course that only lasts half the year. The exception to this is senior year, when colleges will often look at your mid-year grades as you're in the process of applying (and won't really care about your end-of-year grades unless you do really, really badly—like multiple Fs badly).

They'll also look at trends to your GPA over time, so for instance if you have a 3.3 in your freshman year, 3.6 in your sophomore year, and 3.9 in your junior year, they'd pay attention to that as well. A trend that goes upward (like that one) will usually boost your chances, while a trend that goes downward will usually drop your chances, even though you might end up with the same final GPA as someone else.

most schools look at culitive gpa which is end of the year grades on transcript

i believe thats how my school does it