So...I've just gotten my new guitar and I want to make it able to put sound through an amp.

I've already decided that I definitely want to get a Roland Micro Cube amp as it's tiny so it's perfect for my room and it seems like it can do double duty of amping the acoustic AND amping my bass (I'm much more serious about acoustic guitar than bass--so as long as the bass can be heard for my own learning, I'm not really bothered on it).

Anyways, now I need to know how to get the sound from the acoustic to the amp! I've been reading about all sorts of pickups...button, soundhole, undersaddle etc. etc. What I'm not clear on is what I actually should be looking for

Basically, I love my guitar so much that I don't want to change it in any way. Ie: I was going to get a pickup that could be used through installing a strap button jack, but I think my strap button hole would need to be enlarged and I don't want to do that.

Thus, I want an acoustic pickup that will make the sound be heard through my amp, not damage the guitar in any way and preferably be removable even (that way if it's not being used it doesn't have to be on the guitar).

In addition to this, I'm also confused as some of the people in forums have talked about needing preamps as well? I don't even know what that really means. And some of the pickups seems to have what looks like a headphone jack input at the end of them rather than something that would get plugged into an amp. Any idea what that is all about?

Oh man...I feel stupid now
Since I'm assuming that amp is not specifically made for acoustics, I would recommend a soundhole pick up. Dean Markley makes several excellent sound hole pickups. http://www.musiciansfriend.com/navigation/dean-markley-guitar-strings-pickups-accessories-parts-acoustic-pickups-guitar-replacement-parts?N=100001+304424+201033

None of them will require a preamp.

Partscaster/Tele into a bunch of pedals, a Maz 18 head, and a Z Best cab.
Relax, with everything you just mentioned then I'm not surprised you're confused.
Now I'm no expert but what it looks like you are after is a soundhole pickup, i.e. one that sits in the sound hole and works like a pickup in an electric guitar. They usually have some onboard controls, but not always. And some of them have a small plug on them (about a 2.5 or 3.5mm plug that a cable plugs into with a 6.5mm at the other end for connecting to an amp. A mate of mine had one a cheap one of those and it sounded alright. Sometimes with these types there is a problem with excessive feedback from the guitar (cause the pickup has just become part of the resonator of the guitar). To fix this there are pickups that cover the whole sound hole, or you can cover it over with some cardboard or something.
The other types of pickup you mentioned are the piezo undersaddle or underbridge types. They will require modification as you have to replace the bridge, and provide an plughole. Some plugs as you mentioned replace the strap pin at the end of the guitar (my 12 string has that). Also some of these types require a preamp (either onboard or not). The one I've got doesn't need that, so I can just plug straight into an amp and get sound, but I have no onboard volume or tone controls.
As you don't want to modify your guitar I would recommend getting one of the soundhole types (like the other guy said while I was writing this ).