Dear Garden Grove, California:
First, call the Court and obtain a hearing date. It needs to be 14 Court days plus 5 calendar days from the date of mailing of what you are going to serve on the other side that requested the default. Watch the calendar carefully; there are a lot of court holidays coming up. Do not be surprised if the date you are given is two months away. The Court's calendar is crowed.
If you have access to a law library (you are close to Western State University of Law in Fullerton), I recommend that you go and find a current copy of a publication called "Rutter's Civil Procedure Before Trial." It is a three volume set. The instructions on how to do this, as well as the cases that you can cite, will be in the first volume - around chapter 5 or 6. There is probably an example of a Motion for you to follow as well.
Briefly, you are going to be filing a two-part document on pleading (legal) paper. If you use either Word or Word Perfect, there should be a template with lines numbered to 28 on the left hand side, with a double line; and on the right, it will be a single line. Look under Macros or Templates.
In the upper left hand corner, put in your name, address and telephone number.
Starting on line eight, you will put in "SUPERIOR COURT FOR THE STATE OF CALIFORNIA". On line ten, put in "COUNTY OF LOS ANGELES".
The caption will be the identical caption that is on the Request to Enter Default. Make sure to put the correct case number XXXXX the right hand side. The title of the document is "NOTICE OF MOTION AND MOTION TO SET ASIDE DEFAULT JUDGMENT." Below that, still within the caption, put the date, time and location of the hearing.
In the Notice of Motion, you will put: TO THE COURT AND TO THE PLAINTIFF AND ITS ATTORNEYS OF RECORD HEREIN: Please take notice that on (date, time, location) Defendant will move to set aside the Default Judgment entered on _____ on the basis of (put your reason here). Then date and sign the document at this point. [This is the Notice of Motion.]
Put in a hard page break, and start the next section "MEMORANDUM OF POINTS AND AUTHORITIES." This is where you are going to explain what happened (brief statement of the facts); and the law supporting your request (law). You will find that law in the Code of Civil Procedure (http://www.leginfo.ca.gov/cgi-bin/calawquery?codesection=ccp&codebody=&hits=20); look for Section 413.10 if you weren't served with the summons and complaint.
There may be additional reasons besides service of summons the default should be set aside; check Rutters for that information.
Conclude your argument with another date and signature. You must serve the document. You can go to the California Judicial Council for acceptable forms for mail service - it is here: http://www.courtinfo.ca.gov/forms/.