World War I was the first war of any major size after the Industrial Revolution. It was a war of artillery, attrition, industrial capacity, and economic power. The Germans opened the Western Front in August 1914 with the Schleiffen Plan. The plan was to sweep through Belgium and Holland in an encircling movement that was to have the 'Last solder's arm brushing the sea'. The General in command of the German Army, Helmuth Von Moltke, altered the plan to only violate the neutrality of Belgium.
The Germans quickly stomped through Belgium. However, there was stiff civilian resistance, leading to the policy that for every German soldier killed 10 civilians were to be lined up and summarily shot. That order provided excellent propaganda for the allied nations, giving them a cause that could be used to rally the troops.
The German offensive ground to a halt 22 miles to the west of Paris, quite short of the plan's final objective. After the plan ground to a halt, the battle lines stabilized into a front that was virtually locked into place in Northern France.
On the Eastern Front... As soon as the Germans Attacked Belgium, the Russians attacked eastern Germany, in the area where Poland is today. The Russian General Staff was not organized, and in fact, several of the generals were not on speaking terms. As a direct result the Russian infantry was incompetently lead. They were also poorly equiped, and barely trained. The russians managed to entangle many German regiments until 1917 when the Tsar Nicholas II was overthrown. They surrendered to Germany in 1917, at a place called Brest-Livtosk.
The Austro-Hungarians were the worst equiped after Russia, and in order for them to stay in the war until 1918 the Germans had to run their army. They collapsed in Revolt in October 1918.
The Germans sued for peace on October 4, 1918. It took several weeks to agree on an armistice date and time, which was finally set to begin at 11:00 A.M. on November 11, 1918.
This is not an exhaustive description of war, merely a brief overview. If you want something detailed, see:
World War I: A Short History 2ed. by Michael J. Lyons ISBN: 0130205516