Answer: Blogger is an awesome blogging platform where setting up a blog and posting on it is really really easy. when you create a blog on blog you get two options.
1 to stay with free sub-domain .blogspot.com
2 or to get a custom .com domain
using sub-domain is free on blogging and setting up a custom domain costs only around $10 a year.
It is always better to use a custom domain if you want to do blogging seriously to make money or promote your business. if you want to do blogging just for fun then stay with free domain is ok.
using a custom domain will bring more traffic to your blog and visitors will take your blog more seriously.