What is your major? That makes a bit of difference sometimes.
If you do not have at least a couple years of work experience in that field, I would strongly encourage you to forego grad school at this time. Three reasons:
I work with many jobseekers who went straight from undergrad to grad, and now cannot find a job because they are underqualified for the professional positions they seek, due to their lack of work experience, and overqualified, based on education, for the lesser positions which they eventually try to get.
I've had clients who went straight through, and, after working just a few months, realized they were in the wrong line of work.
If you find the right employer now, it is possible you will qualify for tuition assistance to help you with school.
I don't know when to apply. I would check the schools' websites for requirements.
I don't mean to put a damper on your plans, however, education is very expensive and I want to make sure you are aware of the issues that I raised.
Best of luck!