A declaration is your side of the story you want the read. There is a judicial council form (MC-030) that you can use. That form makes it easier to file your declaration. The form has the places for everybody name and the “under of Penalty of perjury” clause.
You need to understand that the court reads a lot of declarations everyday so make yours easy to read. Do not use all capital letters. Double space and run a grammar and spell checker if you have it. As Mark Twin put it "I would have written you a shorter letter if only I had the time". Review your declaration and make it short to the point and effective.
You would then send a copy to the other side and file your declaration with the court with a proof of service that you sent it to the other side.
Attorney Montgomery gives good practical advice. Yes, MC-030 is the correct form. You need to serve a copy on the opposing party and file it with the court.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
If your husband has an attorney, the attorney may be willing to prepare and file a declaration for you. If you are preparing it on your own, you would use MC-030. You would sign under penalty of perjury and it must be served on the wife as well as filed with the court, since you are presumably filing it as evidence for your husband's argument. You will need to attach a proof of service to show that the other side has been served.
The response above does not form an attorney-client relationship. This answer may or may not apply to you and should not be relied upon as legal advice.