1) In the Setting Options, click on Site Contents.
2) Click on new subsite
3) Fill in the details of your new subsite the same way you would for a new site: title, description, URL, language and template.
4) If you wish to have the same user and content permissions as the parent site, click the Use same permissions as parent site radio button. If you wish this subsite to have different permissions than other parts of your site, click on Use unique permissions.
Determine if this subsite will show up in the Quick Launch bar and top link bar of the parent site by selecting Yes or No.
Choose to have the parent site top link bar as this subsite’s top link bar by clicking on Yes, otherwise click on No.
Click Ok. New Blog Library will be created.