GPA is one of the most important objective measures on your college applications. Colleges use it to not only determine your academic aptitude but to compare you against other students in your high school / county. You can increase your GPA by taking Honors or AP classes (depending on the offering your high school has).
Every year the competition for colleges keeps rising so if you're aiming for a school that has very high average GPA's, it's a good idea to start taking these more advanced classes in 10th grade. They have the added benefit of helping you prepare for college since they are more rigorous.
It's totally possible that your school may not offer very many (or any) AP or advanced classes. If that's the case, you can still take classes at a local community college if you'd like. The admissions officers will always look at your application in the context of the resources available to you.
While many colleges consider your application holistically, and don’t have a minimum GPA requirement, some colleges do have a lower limit on your GPA. For example, University of California colleges require California applicants to have at least a 3.0 GPA and nonresidents to have at least a 3.4 GPA (Source).
Often high school students wonder how they can increase their GPA. A lot of it comes down to studying technique. You'll find that even if you take a very intense workload, by following a few key study habits, you can end up doing much better in your classes.