Create the Site
Select Site Actions > New Sub Site.
Select the appropriate site which will fit your needs.
Give the site a title and go to Create.
Setting Permissions on the Site
Once you click create the site will automatically inherit permissions from the above site. Alternatively the permissions for the sub site can be modified in the create wizard by:
Clicking on More Options.
Selecting Use unique permissions > Create.
Now you will be able to set the permissions criteria as per below;
For a list of the level of permissions which can be applied in WSS 2010 please visit WSS 2010 Permissions