Blogging for money isn't easy. You don't just start blogging and the money comes. You generally have to get a following and try to get them to click on ads, or use referral or affiliate links.
But, the best advice is to blog about what you are passionate about such as cooking, watching movies, reading, traveling, photography, crocheting, whatever. Just be knowledgeable about it.
There are online opportunities, but quick money doesn't generally happen. This site has many articles about how to earn money from home.