You have to go through many articles from this site related to your query then you will learn many things about it.
There are many ways to monetize the blog.
1. Advertising networks
Once you have substantial content on your blog, you can register to some advertising networks like Google Adsense, Kontera, Infolinks, etc. and then show advertises of these networks on your blog.
2. Affiliate Networks
You can affiliate to some affiliate networks like Amazon, ebay, flipkart,etc. If your blog is travel related then expedia,etc. and show their ads on your blog. If users buy any of their products by clicking on their advertising from your blog, then you will earn some cut.
3. Your own ad space
You can sell ad space on your blog to advertisers directly.
These are some of the ways for earning from the blog. However, earning depends on number of visitors, page views on your blog and it is a bit difficult to attract so much of traffic from a single blog. So, if you are determined enough to make it big and work with proper discipline, you can earn handsome amounts from blogs.
Following are the best ways to earn from a blog:
Google adsense:(Work on cpc basis):-Hard to approve
Buysellads:(Direct advertisers):Also Hard to approve
Infolinks:(Link intext ads cpc based):Easy
Affiliate like Amazon:depends upon sales
There are number of ways but I have listed the best ones.
I think the above are some ways to earn money from a blog.