The CSS Profile is a bit more complex than the FAFSA since it requires more information from you and your family. It is also much more difficult to make corrections to the CSS Profile once it's submitted, so take your time to fill it out accurately.
Also take note of each college's CSS Profile Priority Deadline (especially if you are applying early) since colleges often have different deadlines. You'll complete the CSS Profile on the College Board website. Like the FAFSA, it opens on October 1st of each year, so here's how you can Get Started with the CSS Profile. For support: