A blog can be many things, it's entirely up to the blogger. A company can run a blog to keep their customers up-to-date on their latest products. An individual can run a blog to tell people about their lifestyle and recommendations, or about things they do.
Sometimes when I'm looking for how to do something, google will send me to a blog describing what I need (and occasionally, that's sent me to one of my own blogs).
To me, my blog is a few things.
It's a record of my life going out geocaching. I could do these write-ups on the geocaching.com web site, but that expects you to write up each cache, whereas to me, a geocaching outing is the whole adventure, and I want to describe that.
It's technical stuff about bike maintenance, computer hardware and software. That might help other people, but it will also help me when I come to do the same thing again in future.
It's essays about matters that I'm concerned about, and which I think other people might be concerned about; politics, ethics, morals and suchlike.
And it's great fun.