A blog can be profitable in a few ways. The first way is through advertising. You can place ads on your blog or you can sell ad space on your blog. This is a good way to make money if you have a large following.
You can also make money through sponsorships. If you have a popular blog, you could become a sponsor for a company and receive compensation for promoting their product or service. Finally, you can make money through the sale of products and services that you recommend on your blog. If people buy what you are recommending, you earn profit.