Most colleges will calculate your GPA using only the grades from your core academic classes. Basically, those are courses in the following:
Math: Three to four years(algebra, geometry, calculus)
English: Four years(composition, literature, speech)
Social Sciences: Three years (history, sociology, psychology, political science, geography, economics
Science: Three years (earth science, biology, chemistry, physics)
Unfortunately, students sometimes struggle in one or more core areas. Some students believe that they can increase their GPA's by taking an elective, such as a Phys Ed class.
While this might give you a confidence boost, you should know that scoring well in an elective class probably wont help when it comes to college entry. Take fun classes to break up the schedule, but don't count on them to pave your way into college.
Remember, it's so important to keep academic grades under control in the early years of high school. If ever you find yourself slipping behind in the important courses, seek help right away. The help is out there!