"The Tascam 414 MK II 4 Track recorder" - I'll try to be as gentle as possible here, since you may have thought you were getting more than what you bought - In the quote from your question above, did you notice it is called a 4 track recorder? This is because that's all the tracks you can record. The other inputs are only extra inputs to the mixer section of the recorder, and can be used to feed extra signals into the mix while you're mixing down the 4 tape tracks to a stereo recorder, such as a minidisk, CD-R, or stereo cassette recorder. This way, you could record 4 tracks, then mix those to 2 track stereo while playing along on, say, a guitar lead or a vocal, etc - The extra tracks could also be used as inputs from a MIDI keyboard, which with some extra gear could be synchronized with your tape tracks to allow more tracks at a time. These MIDI tracks, played back from a sequencer, are also know as "virtual" tracks, because you can change which instrument plays them AFTER they are recorded.
Sorry to be the bearer of bad news, but without extra gear 4 tracks is all you get. It is conceivable to "bounce" tracks and get a few more, but there are noise penalties. When you learn more about your 414 and its basic usage, ask about track bouncing and/or MIDI instruments. Hope this helps... Steve