Both answers are right. A blog can be an online diary where you write about your life or it can be articles or "how to" stuff like make up reviews. Or a lot of people have weight loss blogs where they record their progress.
Also Vlogs are getting very popular, Its like a blod but you video everything and upload it to youtube. Some people record everything they do for the day or highlights and then upload it so the public can see.
I hope that my explanation helps you

This is what Wikipedia says, "A blog (derived from the term web log) is a personal journal published on the World Wide Web consisting of discrete entries ("posts") typically displayed in reverse chronological order so the most recent post appears first. Blogs are usually the work of a single individual, occasionally of a small group, and often are themed on a single subject. Blog can also be used as a verb, meaning to maintain or add content to a blog."

So a blog can be almost whatever you want it to be. My suggestion: pick a topic, draft something up, and post it here. It's really easy and fun. Look over some of the other ones for ideas

Yes thank you =)