Lwjgl OpenGL Help

Question:
Question;
I've made my top-down minecraftlike game to a point. Dynamic/adjustable types, basic entities, player movement, a worldgen...
However.
This whole time I didn't understand that I needed to code the game to use a Video card via OpenGL and stuff, so the game lags like a whore by only using CPU power to display everything.
So, I'm looking into lwjgl(Yes, I'm using Java), and following some tutorials I understand 'kinda' how to draw basic 2D shapes using OpenGL.
However, I am stuck.
There seem to be multiple ways of displaying a graphic?
DisplayLists, and Vertex Buffers?
I have NO idea what I am doing here.
Do I somehow have the video card calculate the layers of images I am making?
Or is it 'purely' for display?
Sorry if the answer seems obvious, but although I know coding enough to do alot of stuff, this OpenGL stuff seems way over my head and I'm not exactly sure what computer logic I am trying to follow.

>>3
Yup. I mean, maybe in the future I might allow the player to travel though space off the planet he is on, and the space travel might be 3D.
however, right now I am just focusing on 2D. Most of all my code will be in 2D.

I would just start small, but I'm not even sure how/where to start. I'm trying to figure out how to process my sprites right and minimize lag, because right now my game gets ~15fps while ingame, and this pc can run gamecube emulators flawlessly, so obviously the lag is from the code somewhere. I assumed it was because of how I am not currently using OpenGL and I could pass some of the work to the Videocard somehow, or something.