In California ONLY
While there are a few different paths a case may take, one typical path would be:
First, you file forms with the Court (perhaps some or all of the following and perhaps others):
In San Diego County: SDSC D-049: Family Law Certificate of Assignment – Venue Declaration
FL-100: Petition for Dissolution of Marriage, Legal Separation, or Nullity of Marriage
FL-105/GC-120: Declaration Under Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA) – Only if you have minor children
FL-115: Proof of Service of Summons
FL-140: Declaration of Disclosure – To exchange with your spouse
FL-142: Schedule of Assets and Debts – To exchange with your spouse
FL-150: Income and Expense Declaration
Second, you have a third party of 18 years of age serve a copy of the Court forms along with blank responsive forms on the other party and file a Proof of Service of Summons with the Court.
Third, you exchange Declarations of Disclosure and file proof of that action with the Court.
Fourth, you negotiate a settlement and file forms with the Court known collectively as a Judgment, Request for Entry of Judgment, perhaps Declaration for Default, Notice of Entry of Judgment, etc. – there is a checklist available here for California cases.