Petitioner files for divorce
Respondent responds (either signing, fighting it or filing a countersuit)
Then parties have to negotiate children's arrangements if they're not in agreement (the courts will not grant Nisi if children are not provided for)
The divorce Decree Nisi is granted (says legally you can divorce, but you are not yet divorced)
Then you can apply for Decree Absolute (legally you are divorced)
Parties can sign documents agreeing finances etc only after the decree Nisi is granted. Most are advised not to apply for the Absolute until everything is settled because it can affect your entitlement to share certain assets. You can block the other party for getting the Absolute if you can show you've not reached financial agreement etc or being divorced would deprive you of benefits not yet negotiated on (ie. health insurance).
So, just beginning things, but on the way there!