After having configured NewsReactor and selected the newsgroups you want to find messages or binaries in, you are able to download files. But first you have to find out what is available on the groups you selected. That process is called scanning a group. What NewsReactor does is download the post headers in that group (a header is the part of a post that contains the title and other useful information about the post, such as whether or not it has files).
Scanning a group
To scan a group, select it in the Group list on the main window and click the Scan button on the toolbar, or press Ctrl+S on your keyboard. Alternatively, you can right-click the group in the Group list and select Scan from the drop-down menu, or choose the Scan entry in the File menu.
After the header download is complete, the posts will be shown in the header list on the main window.
Resetting a group
Everytime you want to update the list of available posts on a group, you just have to scan it again. However, every now and then you should reset a group to remove all headers from the list, so that old headers which are not available anymore aren't shown. NewsReactor tries to find expired posts and remove them everytime you scan a group, but it is always a good idea to reset the group once in a while.
To reset a group, select it in the Group list on the main window and hit Ctrl+R on your keyboard. Alternatively, you can right-click the group in the Group list and select Reset from the drop-down menu, or choose the Reset Group entry in the File menu.