The Triple Entente was created in reaction to the forming of the Triple Alliance, and included Britain, France and Russia.
An alliance was formed between Russia and France in 1894. By 1904 Britain began talks with Russia and decided that it should come out of its 'splendid isolation', joining the Entente Cordiale ('Friendly Agreement'). By 1907, Foreign Minister Sir Edward Grey negotiated Britain into the Triple Entente, and united three old enemies. In contrast to the Triple Alliance, the terms of the Entente did not require each country to go to war on behalf of the others, but stated that they had a 'moral obligation' to support each other.
France and Russia had fought the Napoleonic wars, and France and Britain had been fighting off and on for hundreds of years. Russia and Britain were also cautious partners as Britain was allied with Japan who had defeated Russia in 1904. All three had been in competition for colonies in Africa, Asia and the Middle East. But all were united in their suspicions of German plans to dominate Europe.
Rather than discussing plans and settling disputes, most countries in Europe sought peace through military superiority. No one would attack the country with the largest army and/or navy, because they knew they couldn't win. The Entente was created to balance the growing power of Germany by being more powerful itself.
Smaller alliances were happening between individual countries all over Europe. The Treaty of London, signed in 1867 long before the Entente, agreed that Britain would protect Belgium's right to be neutral in a European conflict. Italy had signed a secret treaty with France agreeing that they would not attack each other. Russia had signed an agreement promising to protect Serbia. The complicated and unstable system of alliances and conflicting secret treaties crashed down in July 1914.