Sen. A: I yield for a question from my good friend Senator B. Through this “friendly yielding for a question” a single Senator can continue his filibuster for quite a long time while his or her allies are doing the speaking for much of that time.
http://keithhennessey.com/2013/03/07/filibusters/
These apply at any time you are recognized to speak on the Senate floor but are particularly important during extended debate. 1  You can’t sit down. 2  If you do, you have yielded the floor and the Chair will recognize someone else to speak. 3  You can’t eat on the Senate floor. 4  You can drink water or milk, nothing else.
http://keithhennessey.com/2013/03/07/filibusters/
A filibuster occurs when opponents of a bill use obstructive speech  tactics to keep a bill from being put to the vote in the US Senate.  The speaker can talk as long as the … y wish on whatever subject they  want unless three-fifths of the Senators brings the debate to a  close by invoking Cloture. JD Heyl.
http://www.answers.com/Q/Why_might_a_senator_choose_filibustering_as_a_tactic_to_block_a_bill
While Democrats are close to a nearly unassailable 60-seat majority in the U.S. Senate, their numbers can't guarantee the easy passage of the controversial $829 billion health carereform bill that Senate majority leader Harry Reid plans to move to the floor in the coming weeks.
http://content.time.com/time/politics/article/0,8599,1933802,00.html
In 1994 Senator Lieberman, then a Democrat, called the filibuster an obstacle to accomplishment and a symbol of a lot that ails Washington today.. Today Lieberman, now an independent, backs Republicans on health care reform and plans to filibuster the bill when it makes it to the Senate floor.
http://content.time.com/time/politics/article/0,8599,1933802,00.html
A filibuster is a tactic in the legislative process sometimes used in the U.S. Senate by opponents of a bill to block its passage. A Senator, once granted permission to speak by the presiding officer, may continue to speak indefinitely in an effort to delay or prevent a final vote on the bill. To halt the filibuster, the Senate must pass a cloture resolution by a three-fifths majority (60 votes). Filibusters are not allowed in the House of Representatives because House rules limit the time allowed for debate on bills. Bills considered in the Senate under the  budget reconciliation  process are not subject to filibusters.
http://usgovinfo.about.com/od/uscongress/a/filibuster.htm
How a filibuster works. A filibuster is probably better labeled extended debate. To filibuster a question, there isn’t some formal procedural move you make. You simply get recognized by the presiding officer to speak on a debatable question, start speaking, and don’t stop. You talk, and talk, and talk, and talk.
http://keithhennessey.com/2013/03/07/filibusters/
But the Senate dropped this provision in 1806, leaving open the potential for a filibuster. The first filibuster in U.S. Senate history began on March 5, 1841, over the issue of the firing of Senate printers, and lasted six days.
http://content.time.com/time/politics/article/0,8599,1933802,00.html
The longest uninterrupted filibuster on record belongs to South Carolina Senator Strom Thurmond, who stopped a vote on a 1957 civil rights bill for 24 hours and 18 minutes. A filibuster is often an effort of several Senators, but can also be done by a single Senator. The only way to stop one is by invoking cloture  which forces a vote to take place. Cloture, adopted in 1917, used to require two-thirds of the Senate to agree to stop the talking.
http://content.time.com/time/politics/article/0,8599,1933802,00.html
Last night Senator Rand Paul from Kentucky led a 13-hour filibuster of the nomination of John Brennan to head the CIA. Based on a couple questions from friends I’d like to explain how a filibuster works and why they are so rare.
http://keithhennessey.com/2013/03/07/filibusters/
why would a senator use a filibuster as a tactic to block a bill
A senator would use a filibuster to block its passage as a tactic to block a bill. A senator would use a filibuster as a tactic to block its passage.