don't you have a textbook?
well from what i can remember:
they had this thing called the schlieffen plan right which was aimed to attack france quickly so that they could divert their forces to russia so that they didnt have to fight a war on 2 fronts...
anyway, schlieffen died and some dude called moltke went and fiddled with the plan and it got all stuffed up and didnt work out very well and turns out that both sides end up stuck in trenches and dont really know what to do with themselves.
see there was all this new weaponry by ww1 and none of the generals and stuff were really used to dealing with it... eg they had all this cavalry and stuff but it didnt really help them with machine guns and bombs and all.. they were all used to using old tactics but surprise surprise they didnt work anymore. eg. battle of verdun.. they wanted to 'bleed the french white' or something like that... it turned into a war of attrition (wearing the other side down)
also the terrain they were on was perfect for digging trenches>> stalemate
and the weather was bad eg. passchendale... was all wet and muddy and crap... not really that good for fighting
bah, i cant remember... my notes are in the room next door but i cant be stuffed getting them... good luck