They have four possible scopes / levels

 

Farm- at the Farm level

Web application-  at the Web application level 

Site-  at Site Collection level 

Web-  at Single site level

 

A farm level feature is something that affects the whole farm, for example provisioning a custom timer job or deploying a Business Connectivity Services model.

 

A web application feature can be activated so that it only affects a single web application, and a typical example is a feature that modifies the web.config file.

 

A site scoped feature can be activated so that it only affects a site collection, an example being the deployment of a master page to the master pages catalogue.

 

Finally, a web scoped feature can be activated for a single site, for instance setting the default master page for that site.

                        SPListItemCollection collListItems = null;
                        foreach (SPFolder subFolder in oList.RootFolder.SubFolders)
                        {
                            if (subFolder.Name.ToLower() == FolderName.ToLower().Trim())
                            {
                                SPQuery oQuery = new SPQuery();
                                oQuery.Query = "<OrderBy><FieldRef Name=’Modified’ Ascending=’False’ /></OrderBy>";
                                oQuery.Folder = subFolder;
                                collListItems = oList.GetItems(oQuery);
                                break;
                            }
                        }
                    }

For your issue, I recommend to follow the steps as below: