Short answers, pulled from the story.
The Auld Alliance was formed on the 23rd of October 1295, when Scottish envoys agreed to the Treaty of Paris with Philip IV of France. The alliance was directed against England and stipulated that if either country were attacked by England, the other would invade English territory.
The alliance was signed by John Balliol on the Scottish side and Philip IV of France. It was negotiated by a Scottish embassy that travelled to France in October 1295 following dynastic turmoil in Scotland after the death of Margaret, the Maid of Norway.
Between 1419 and 1424, as many as fifteen thousand Scottish troops were sent to France at the request of the Dauphin Charles VII. Scottish and French forces won together at the Battle of Baugé in 1421, and Scots fought alongside Joan of Arc at the relief of Orleans in 1429. Scottish soldiers also served in the Garde Ecossaise, the personal bodyguard of the French crown.
The Auld Alliance is considered to have ended with the Treaty of Edinburgh in 1560, when Scotland's Protestant Reformation led the Lords of the Congregation to reject the alliance and seek English support instead. The marriage of Mary, Queen of Scots to the future Francis II had briefly revived the alliance in 1558, but Francis died prematurely in 1560.
The Auld Alliance affected Scottish architecture, law, language, and cuisine. Scottish castles including Bothwell and Kildrummy were built with French construction in mind. Many Scots studied at French universities, and notable figures including the poets John Barbour and George Buchanan, historian Hector Boece, and the founders of St Andrews University and Aberdeen University all studied or taught in France.
In a speech delivered in Edinburgh in June 1942, Charles de Gaulle described the alliance between Scotland and France as the oldest alliance in the world. He declared that in every combat where for five centuries the destiny of France was at stake, there were always men of Scotland to fight side by side with men of France.