Without a country of origin, it's very hard to walk you through the legal process, as different countries have different chains of evidence, etc. Prefacing with NAL, but I do have experience with trafficking and advocacy groups.

Assuming you're in the US, This is a very straightforward and undetailed process of what will most likely happen is when you go in to file a police report, they will sit you down and interview you. Expect to be heavily questioned on why it's taken you years to report the abuse. After they take the report, the next step would be to begin an investigation into the claims, where they will collect evidence. After they have collected said evidence, they will pass their case along to the Distict Attorney, who will then decide, based on the merits and collected evidence, if there is sufficient evidence to go to trial.

I would suggest asking your therapist if they are aware of support groups for survivors of child abuse in your area, or other survivor advocacy groups, as they can help you better prepare for what's ahead from a legal, as well as mental and emotional, standpoint. Good luck to you.