In this Blog I have describe that how to access sub site from authentication user or group. First of all we need to create a sub site in site content. For doing this I have describe following steps to create a sub site in SharePoint.
Step for creating a sub site in SharePoint 2013:
1- On your team site or web site, click Settings, and then Site Contents.
2- On the site contents page, under sub sites
3- Click a new sub site page
4. Click on new sub site button. Open’s a following page on screen
5- If you select use same permission as parent site, on set of user permission shared by both sites.
6- If you select use unique permissions and click the create button, following page open as shown below in screen shot
7- Site already has three group created in it as Visitor, Members and Owners.
8- If you select create a new group, enter a group name in the text box.
a. After that assign the more than one user to this group.
b. Click the OK Button
9- If you select use an existing group.
a. Select an existing group on dropdown list.
b. Register user permission to assign to this group of sub site.
c. Click OK Button
So later when you login with existing user it will be register with this Group Permission for this site.