A blog is something you write on the internet, almost like a journal. It can be news, your personal life, just you complaining about random stuff, anything. Tumblr is a blogging service but in shorter chunks. Like a picture? Post it on tumblr. Blogspot or blogger is a more in depth blogging service. Like if you want to write a few paragraphs or a few pages of material. And Twitter is a micro-blogging service. Just for what happens in your life, an interesting article you like, a joke. The small stuff.