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.

>>6
Maybe. Computers weren't always fast, and video cards didn't always exist, but people still managed to (very creatively) make games for them. Is the frame rate proportional to the number of entities, etc, currently on the screen? If so, then open gl can help with that. If performance is still bad, then maybe you're using an O(n^2) algorithm somewhere in the code that updates the world.