Good idea, and welcome!
A seeder is someone who is making a video available to upload. Leeching is someone downloading it (who can then become a seeder when they have it complete)
An ISO file is a complete `image` of a DVD - including all video, audio, menu screens etc. - if you copy an ISO to a blank DVD you have a complete disc, complete with animated menus, multiple chapters / videos etc.
the video_ts is the video part of a DVD disc. Guess what the audio_ts part is!
Finally, codecs are data files installed on your PC that allow you to play different formats of videos; eg WMV, MPEG 1,2 and 4, .mov, divx etc. Windows comes with some basic ones for WMV, MPEG1 etc. but you have to install others yourself for the more exotic ones like divx files - all codecs are usually free to download, apart from MPEG2 (needed to play a DVD on your PC) which tend to need liscensing for a small one off fee.