It records the TV Series that you tell it to record in the Recording Rules.
That could include only new episodes of a series, and not repeats (reruns), if you like. Or episodes that haven't been recorded by MC before. Or all episodes on one channel, or a list of channels, or all channels. Or just one episode per week, or per day, near a particular timeslot, or in Prime Time, or the "middle of the night". You can set up simple or complex rules for selecting programs to record, and you can even specify a preference for HD recordings, if a program may be shown on a SD and a HD channel at the same time.
The rules are very flexible. However, a lot of the functionality relies of the EPG data, and its quality, including completeness of the EPG, and whether certain tags are included, such as the Repeat flag, Season and Episode numbers, and whether a channel is HD, in particular.
If there is enough information in the EPG to find a program in TheTVDB, then MC will save TheTVDB ID for the series, and then all future episodes of that series will be assigned that ID, and will be grouped in MC, and future lookups of TheTVDB will use that ID to find episodes. That, of course, is done after the program has been recorded. If your EPG data source has TheTVDB ID included in it, then Series and Episode matching is much better.
The recording rules functionality has changed a lot over the last year or so, and the Wiki hasn't kept up with all the changes, so best to search this forum for discussions on the rules. Or just start using them and see what you can achieve with them.