No stupid questions here; welcome to what will likely be your new obsession, er, hobby!
Looking at the pictures and description, I'm wondering if there is a gasket under the bucket lid. If not, it's likely not air/co2 tight and will easily dispel the built up pressure. If there is a gasket, boulderbrewer is right on the money with the advice to just loosely affix the lid.
Good luck and have fun!