LOL, anything is going on...
The thing is that they set monuments (don't really know how to explain the materials in English, but among other things they have would, paper, cartoon...) and these monuments are quite satiric, they have scenes (in many cases) criticising some local (or national) political or whatever 'affairs'. These monuments are on the streets (in the city of Valencia and in other vilages near Valencia) so that people can see them (there are many monuments, some good, and the rest of them are much smaller, and the quality is much poorer). So, there's a competition, and there's a ranking of Fallas in each category.
Later, on 19th March, all these Fallas are burned (many people outside Valencia criticise that, but...what would be the Fallas if they weren't burned later?
). It's supposed to symbolise that the bad things that had happened during the year 'disappear' with the fire
(btw, the pronunciation of Falla is very similar to the pronunciation of fire).
Appart from this, there are other things: the offer of flowers to the Virgin (where falleros (people with regional clothes..) bring flowers), music concerts, and my fave thing...mascletà, that's lot's of 'firecrackers' (they are called masclets) exploding together, and they make BIG noise, and this is at 14 everyday from 1st March till 19 March; there are also fireworks...
Well, it's being tiring to explain all this, lol