The world wars from the twentieth century seem to be very complex events, but in reality, there are long periods of time where the fronts were relatively stable. It is only during specific operations that fronts tend to move. Thus, I'll try to summarize the war, and interestingly enough, June of 1944 was not that interesting, and not even July, but rather, it was not until August that the Allies broke out of Normandy and began to make a significant impact in France. In some cases, I've simplified the start and end periods, especially if they only spread a few days into a given month. Please see this excellent video by Emperor Tigerstar.
The events are color coordinated with blue representing the west and northwest, red the east, and gold representing Italy, the Balkans and Africa (the south). You will note that on most fronts, there are long periods (months if not years) before a major operation begins to move the front. Essentially, what this is suggesting, is that modern warfare is, while having continuous contact between combatants on the front lines, an endeavor that requires significant build-up of materiel and forces before significant progress can be made. Skirmishes may achieve minor shifts to the front line, but the breaking of a static defence requires a significant concentration, and once the front is broken, it is subsequently easier for the attacking forces to continue the momentum, for once the front-line defences are breached, any subsequent defences thrown up will necessarily be sub-standard; that is, until a prepared defensive line (such as the Gustav and Gothic Lines in Italy) or significant rivers or other barriers (such as the Vistula in Poland) sufficiently hamper the depress the momentum of the attacking force.
Each month is generally two lines, so you are able to also estimate the relative time between events.
September, 1939
Germany conquers most of Poland (Plan White), while the Soviet Union conquers the eastern third.
December 1939 - February 1940
Failed Soviet Union invasion of Finland.
April, 1940
Germany conquers Denmark and Norway (Operation Weser Exercise).
May and June, 1940
Germany conquers the Low Countries and France (Plan Yellow followed by Plan Red).
June-July, 1940
The Soviet Union invades the Baltic States and then part of Romania.
November, 1940
Greece joins the Allies while then Hungary and Romania join the Axis.
January-February, 1941
Allies push into Libya from Egypt.
April, 1941
Germany conquers Yugoslavia and Greece (Operation 25) and reconquers Eastern Libya (Operation Sunflower), with Crete falling in June (Operation Mercury).
June-November, 1941
Germany invades the Soviet Union up to the Rostov-Moscow-Leningrad line (Operation Barbarossa followed by Operation Typhoon).
November, 1941
The Allies recapture Eastern Libya.
January, 1942
The Soviet Union pushes back to the Rostov-Leningrad line.
January-February, 1942
Germany recaptures Eastern Libya.
June-July, 1942
Germany invades Egypt (Operation Surf).
July - August, 1942
Germany invades the Caucuses (Plan Blue).
November, 1942
The Allies invade Algeria (Operation Torch) and recapture Eastern Libya.
December 1942 - February 1943
The Soviet Union takes Stalingrad (Operation Uranus) and pushes Germany back to the Rostov-Leningrad line (Operation Saturn).
January - April 1943
The Allies take Africa.
July 1943
Battle of Kursk (Operation Citadel) and Allied conquest of Sicily (Operation Husky).
August-October 1943
The Soviet Union pushes Germany back to the Crimea-Leningrad line (Operations Kutuzov and Rumyantsev).
September 1943
Allies conquer Italy just beyond Naples (Operation Avalanche) up to the Gustav Line.
January - April 1944
The Soviet Union liberates Ukraine and pushes into Romania in the south (Dnieper–Carpathian Offensive).
May-July 1944
Allies conquer the Italian peninsula up to the Gothic Line starting with Operation Shingle in January, 1944.
June - July 1944
Allies recapture Normandy (Operation Overlord).
July-August 1944
The Soviet Union advances into Poland in the north (Operation Bagration).
August-September 1944
Allied liberation of France and Belgium (starting with Operation Cobra, and Operation Dragoon in the south).
September-December 1944
The Soviet Union conquers Romania, Bulgaria and the Balkan Peninsula.
September - November 1944
The Soviet Union invade the Baltic (Baltic Offensive).
November - December 1944
The Allies push towards the Siegfried Line (Operation Queen starting earlier with the Battle of Hürtgen Forest).
December 1944 - January 1945
The Germans counterattack in the Ardennes (Operation Watch-on-the-Rhein) but are slowly pushed back to the Rhein.
January 1945
The Soviet Union pushes towards the Oder River (Vistula–Oder Offensive).
February - March 1945
The Soviet Union conquers Poland and Germany up to the Oder.
March-April 1944
Allied cross the Rhein and invade Western Germany (Operation Plunder) pushing up to the Elbe River.
April 1945
The Soviet Union crosses the Oder River and attacks Berlin (Berlin Strategic Offensive Operation).
April 1944
Allied push south into Bavaria.