There are four groups of connectors (Line A, Line B, RGB/Component, and Ext Sync), and each group should be treated as a whole.
As it's a monitor, I assume you have an "out" for each "in", and the "out" is just connected to the corresponding "in" (because "out" otherwise doesn't make sense for a monitor).
You'll be able to choose between three sources, "Line A", "Line B", and "RGB Component". "Line A" accepts both S-Video (Y/C) and Composite (Video) in addition to audio, "Line B" only accepts Composite (Video) in addition to audio, and "RGB/component" accepts either RGB or component (R-Y/Y/B-Y) in addition to audio. You'll be able to select for the latter which type it is.
In addition to everything, there's the option to have external sync signals (whatever kind, you'd need the manual for that).
So when I have a Composite Cable with Video/L/R means, I put the cable into Video IN (Line A) and Audio In (Line A+B)?
It means you decide if you want to connect it to "Line A" or "Line B", and then you connect it to "Video" and "Audio In". Say you connect it to "Line A", then you can connect a second composite signal from some other computer to "Line B".