Why the Japanese didnt help out with fighting the Russians? (As they could have come from the other side? )?

Question:

who they were even fighting really during WW2 before Americans and where? and how their military was in comparison to Japanese military?

Answer:

The Japanese already were fighting a two front war.
They were fighting in Manchuria China begining in 1933 - long before any other country even heard of WW2. Hitler signed a non aggression pact with Russia in 1939 so at no point was Russia an enemy of Japan - not until the Germans invaded in june of 1941 at which point Russia switched from being allied with the Axis to being allied with the Allies. At that point in time [keeping in mind the Japanese were still fighting in Manchuria] they also attacked Britain colonies in the South Pacific and the Americans at Pearl Harbour - among other places.
So Russia didn't become an enemy until 1941, when Japan was fighing in China, against Britain, against the USA - so they already had plenty of second fronts [lol].

Actually in not attacking Russia the Japanese helped out the Russians in more ways than one.
The Russians expected a Japanese attack, the two countries had border skirnishes prior to WW2 that Japan mostly won - so the Russians during WW2 were expecting more of the same. The Japanese never did though.
Then the Germans attacked Russia and kicked butt all the way to the suburbs of Moscow, many felt Moscow would fall as it wasn't defended well. Stalin's spies told him the Japanese aren't a threat nor plan to invade... and this was one of the rare times Stalin believed his spies. He moved his Siberian troops away from their positions near Japan and put them in Moscow instead - they did much to prevent the Germans from taking Moscow, stopped the Germans cold and halted the 1941 Barbarossa offensive.