Step 1 is the easiest and least expensive Step. This is just the beginning of the process but it does need to be done correctly.
You start by determining what you need to file. Are you married? Then an Original Petition for Divorce? Not married but have children? Then it is a Suit Affecting the Parent-Child Relationship. Want to change an existing custody order? Then you'll need to file a Petition to Modify the Parent-Child Relationship. There are many other types of filings.
Then you must decide where (what County) to file. Usually everyone involved live in the same County and it is a simple decision. If there is a Modification then you must usually file where the underlying order was filed. There are more complex rules involving multiple states (in the UCCJEA) as well as international cases. Here are more detailed rules:
Here is how we illustrate these 5 Steps for a divorce.