What is posted to a mailing list gets posted to the newsgroup and vice versa. Thus, you have the choice of receiving posts as email messages or as Usenet articles. Email has the advantages of generally being faster and not requiring that you have a newsreader. With newsgroups, you have the advantage of not having to subscribe or unsubscribe, and of downloading only those messages which you want to read. More so than in mailing lists, you'll find a lot of noise in some newsgroups.
Spams are off-topic postings, posted inappropriately to many different newsgroups.
Flames are insults directed at individuals and add no value to the group. On the other hand, some news groups have very little noise and you can find a great deal of valuable information. When you first use a newsreader, it downloads a list of all newsgroups available on your news server. How the newsreader stores that list depends on the news program. It may be in a proprietary database format or it may be in a file called newsrc.