WHO
The English and the French.
WHAT
Okay so basically it was fights over land in France that the English had long claimed as their own.
The English won most of the early battles of the war, and the English army was made up of lightly armored soldiers with longbows. The French army relied mostly on knights carrying crossbows. But the long bow was more effective than the crossbow due to it's superior range. Later in the war, the French began to use more modern tactics.
WHEN
1337 to 1453
WHY
English claimed lands in France were their own, but the French King disputed this claim believing these lands were their own. When King Philip VI of France said this land was a part of his realm, war broke out in France.
JOAN OF ARC
Joan of Arc was a women during this war, and she heard a message from the saints telling her to save France. In 1429 and at age 17, she led the French Army to victory in the Battle of Orleans. The next year, the English took her captive and burned her alive on a stake, claiming she was a witch and a heretic. Despite this, she inspired the people of France to fight for their country, and gave the citizens a sense of unity which helped them win the war.