1, Complete the C4...you will need to state the persons or agencies you wish to be part of the order - ie who is to disclose the ex's whereabouts? This could be perhaps the school, an employer, DVLA, Housing Benefit, GP, a solicitor who was previousely acting for your ex.....
2, You go to county court. Submit the form and see the Clerk. Explain you wish to see a Judge on an ex-parte basis that day.
3, Wait...perhaps hours.
4. When your in front of the Judge you will need to explain why the order is needed. For example, you need to serve papers in respect to contact arrangments and have no address.
5. Wait...for the order to be typed up...could be hours.
6. Serve the order on the parties named. If they are private individuals you may need a process server. If they are organisations then first class post should suffice.
7. The order requires the named parties to tell the court your ex's contact details (not yourself). You therefore have to periodically check with the court to see if responses have been recieved.
8. Once the court have contact details for ex...you would then be able to initiate other court proceedings (asking the court to effect service of papers on the ex until such time as the court agrees to disclose her address to you).