Short answers, pulled from the story.
The Triple Entente was an informal mutual arrangement between the Russian Empire, the French Third Republic, and the United Kingdom of Great Britain and Ireland. Unlike a formal military alliance, it imposed no binding obligation of mutual defense and was described by British Foreign Office official Eyre Crowe as "nothing more than a frame of mind."
The Triple Entente was built on three agreements: the Franco-Russian Alliance of 1894, the Entente Cordiale of 1904 between France and Britain, and the Anglo-Russian Entente of 1907. The 1907 accord resolved long-running disputes over Persia, Afghanistan, and Tibet and ended the rivalry in Central Asia known as the Great Game.
By the early 1900s, the growing threat from Germany led Britain to seek allies. London first approached Berlin, but those overtures were not reciprocated. Britain then signed the Entente Cordiale with France in 1904 and the Anglo-Russian Entente in 1907, ending the policy of splendid isolation it had maintained through the nineteenth century.
No. The Triple Entente was not an alliance of mutual defense, which distinguished it from both the Triple Alliance and the Franco-Russian Alliance. Britain remained free to make its own foreign policy decisions in 1914. All three members entered World War I as Allied Powers, but that outcome was not guaranteed by any binding treaty obligation.
British war minister Lord Haldane traveled to Berlin in February 1912 to reduce friction from the Anglo-German naval arms race. The mission failed because Germany demanded a British promise of neutrality in any war where Germany was not the aggressor, a condition Britain refused. Historian Zara Steiner noted that accepting it would have meant abandoning the entire entente system.
On the 4th of September 1914, the Triple Entente issued a declaration undertaking not to conclude a separate peace and to demand only terms agreed upon by all three parties together. This was a significant commitment given that the Entente itself carried no formal treaty obligation of mutual defense.