me being clueless

what is a blog exactly ? do you just write your thoughts or things that happen or does it not matter? i mean yeah nothing really matters cause it’s my blog so can put whatever i want but what is the intention of a blog? this might me a simple common sense answer but i’m a little slow and lack common sense unless things are explained very thoroughly 

(the category thing just helped, nvm guys i’m no longer that clueless)