FAFSA will be delayed again for most families this year, but it is relatively easy to complete (IRS tax info automatically imports.) Follow developments on this thread: Phased rollout for 2025-26 FAFSA
CSS is much more detailed and costs money to file, and required by many schools that give relatively generous financial aid. Look to each school’s website to see what they require. Here’s a complete list (but verify on each school’s site because it’s not updated for 2025-26 yet.)
https://profile.collegeboard.org/profile/ppi/participatingInstitutions.aspx