When a suit is instituted by the plaintiff the court orders to issue summons to the defendant. This is to permit the defendant to appear and answer the claim of the plaintiff. This ensures a fair trial. Without a duly served summons no further action can be taken against the defendant. So sending of summons is very important in a civil case.
Section 27 and Order 5 of the Code of Civil Procedure deals with the service of summons to defendant. As per section 27 the summons may be served on such day not beyond thirty days from the date of the institution of suit. Now you should look at the provisos of Order 5 Rule 1 of CPC. No such summons shall be issued when a defendant has appeared at the presentation of plaint and admitted the plaintiff's claim. So inorder to attract this proviso the defendant must appear and as well as admit the claim.
Every summons shall be accompanied by the copy of the plaint also. I shall give details regarding how the summons is served in another post. Thanks.