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