First you have to make website on WordPress to make blog or you can sign up on blogger which is Google product.
After your website ready then sign in to website then go to dashboard and click on the post.
In post click on add new post and start writing blog.
Now, how to monetize blog?
First you have to sign up for Google AdSense by using your URL.
After that you have to copy code display in front of you on AdSense site.
There are two method for adding AdSense code on your site.
One manual method other is plugging method.
In manual method go to dashboard of your site click on appearance then click on editor.
In editor click on theme header and search for <head><meta> tag..
Paste the AdSense code in between head><meta and click on save button at bottom.
Now, come back to AdSense page and click on submit and finish.
In plugging method – go to dashboard then go to plugging and click on add new. Search for insert header and footer plugging, install it and then activate.
In this plugging you will find two boxes one is header and others is footer.
You have to paste the code on header box and submit it.
After this AdSense mail you for your site ready for ads.