Pleadings, motions, discovery and other case documents are required to be "served" on parties in a lawsuit. This simply means that everybody gets a copy of everything. There are rules that govern how these things are "served" or, in plain English, are sent. The rules differ by state and court system. Here are links to the California rules:

Notices (CCP 1010-1020)

When to give notice or file opposition (CCP 1005.5) ("Unless otherwise ordered or specifically provided by law, all moving and supporting papers shall be served and filed at least 16 court days before the hearing.  The moving and supporting papers served shall be a copy of the papers filed or to be filed with the court.  However, if the notice is served by mail, the required 16-day period of notice before the hearing shall be increased by five calendar days if the place of mailing and the place of address are within the State of California, 10 calendar days if either the place of mailing or the place of address is outside the State of California but within the United States, and 20 calendar days if either the place of mailing or the place of address is outside the United States, and if the notice is served by facsimile transmission, express mail, or another method of delivery providing for overnight delivery, the required 16-day period of notice before the hearing shall be increased by two calendar days.  Section 1013, which extends the time within which a right may be exercised or an act may be done, does not apply to a notice of motion, papers opposing a motion, or reply papers governed by this section.  All papers opposing a motion so noticed shall be filed with the court and a copy served on each party at least nine court days, and all reply papers at least five court days before the hearing. [Par.] The court, or a judge thereof, may prescribe a shorter time."

Electronic service (Cal. Rules of Court, Rule 2.260)

Direct filing of document in court (Cal. Rule of Court, Rule 2.304)

Requirement for signatures on documents (Cal Rule of Court, Rule 2.305)

Service by fax (Cal Rule of Court, Rule 2.306)

Small Claims Court

"How to Serve a Business or Public Entity (Small Claims)" - by the California Judicial Council

Superior Court of California - Service of Summons and Complaint

Service on defendant who is outside California but within the USA

California Code of Civil Procedure § 413.10

Except as otherwise provided by statute, a summons shall be served on a person:
. . .
(b) Outside this state but within the United States, as provided in this chapter or as prescribed by the law of the place where the person is served.

§ 415.20
(b) If a copy of the summons and of the complaint cannot with reasonable diligence be personally delivered to the person to be served as specified in Section 416.60, 416.70, 416.80, or 416.90, a summons may be served by leaving a copy of the summons and of the complaint at such person’s dwelling house . . . in the presence of a competent member of the household . . . at least 18 years of age, who shall be informed of the contents thereof, and by thereafter mailing a copy of the summons and of the complaint (by first-class mail, postage prepaid) to the person to be served at the place where a copy of the summons and of the complaint were left. Service of a summons in this manner is deemed complete on the 10th day after the mailing.

§ 415.40
A summons may be served on a person outside this state in any manner provided by this article or by sending a copy of the summons and of the complaint to the person to be served by first-class mail, postage prepaid, requiring a return receipt. Service of a summons by this form of mail is deemed complete on the 10th day after such mailing.

§ 416.90
A summons may be served on a person not otherwise specified in this article by delivering a copy of the summons and of the complaint to such person or to a person authorized by him to receive service of process.

§ 417.20
Proof that a summons was served on a person outside this state shall be made:
(a) All proof of personal service shall be made on a form adopted by the Judicial Council.
. . .
(c) Subject to any additional requirements that may be imposed by the court in which the action is pending, in the manner prescribed by the law of the place where the person is served for proof of service in an action in its courts of general jurisdiction; or
(d) By the written admission of the party.
(e) If served by posting pursuant to Section 415.45, by the affidavit of the person who posted the premises, showing the time and place of posting, and an affidavit showing the time and place copies of the summons and of the complaint were mailed to the party to be served, if in fact mailed.

Proof of Service of Summons - California Court Form

http://www.courts.ca.gov/documents/pos010.pdf