Each school is different, but basically if a course is transferrable it will be calculated in your GPA, the question may be what courses are or are not transferrable. Have you called the admissions office or looked online for your target universities, or does your current school have any transfer guidance materials? They likely have this information available somewhere, usually calling an office will result in getting what you need.
Your transcript from your current college should have your GPA calculated for you, so there shouldn't be too much that you need to manually calculate unless you have a lot of courses that won't end up transferring. The basic process (or so I have seen on a consistent basis) is to take the grade points earned and multiply that by the total number of credits for that course. You add all of those up for each course and then divide by the total number of units attempted/completed.
English 3 sem. hrs. A- = 4.0*3 = 12
History 3 sem. hrs B = 3.0*3 = 9
Spanish 5 sem. hrs A = 4.0*5 = 20
Total gradepoints: 12+9+20 = 41
Total hrs attempted: 3+3+5 = 11
GPA: 41/11 = 3.727
Some schools don't stick to just 4.0, 3.0, etc., and instead have values like 3.67 assigned for an A- and 3.33 for a B+, but if your current college doesn't assign grades on a +/- scale, you can use the traditional scale.