I'm sure this answer skips many many details and exceptions (so take with salt and if you disagree or have something to add, leave a comment :P), but... Each OpenGL version mostly just adds features, so if you start using a new features it might limit the hardware you can run your app on (and so the question attracted a downvote, when instead it should have attracted an explanation).
Basic drawing pretty much remains a constant, with one very big exception: all the stuff that was deprecated in version 3 and removed in 3.1.
Old, < GL 3:
We used to be able to do things like:
glEnable(GL_LIGHTING); //fixed-pipeline lighting. replaced with shaders
glEnable(GL_TEXTURE_2D); //fixed texturing
glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glTranslatef(...); //builtin matrices
glBegin(GL_TRIANGLES); glVertex3f(...) ...; glEnd(); //immediate mode with per-vertex calls
glVertexPointer(..., myArray); glDrawArrays(...); //immediate mode with client side array
But even then we still had GLSL shaders and VBOs. There's a fair amount of overlap and the GL3 deprecation didn't instantly replace everything:
glBufferData(...); //buffer mesh data to bound VBO
...
glVertexAttribPointer(...); //attach data to myCustomVar (either VBO or immediate mode local array)
...
attribute vec3 myCustomVar;
varying vec3 myVarying;
...
gl_Position = gl_ProjectionMatrix * gl_ModelviewMatrix * gl_Vertex;
...
gl_FragColor = vec4(1, 0, 0, 1);
New, >= GL 3:
The new way of drawing removes immediate mode and a lot of these in-built features so you do a lot from scratch, adds a few features and syntax changes. You have to use VBOs and shaders:
glBufferData(...); //buffer mesh data
...
glVertexAttribPointer(...); //attach VBOs, but have to set your own position etc too
...
#version 150 //set GLSL version number
out vec3 myVarying; //replaces "varying"
gl_Position = myProjection * myModelview * myPosition;
...
in vec3 myVarying;
out vec4 fragColour; //have to define your own fragment shader output
...
fragColour = vec4(1, 0, 0, 1);
To answer your question, and this is completely my opinion, I'd start learning GLES2.0 (afaik pretty much a subset of GL3) because it's so well supported right now. GL2/immediate mode certainly doesn't hurt as a learning step, and there's still quite a lot that isn't deprecated. You can always just use GL 4 features if you find you need them, but as said the basics really only changed between the above versions. Even if you use deprecated features you have to go out of your way to get a pure GL3.2 (for example) context that disallows certain calls/features. I'm not advocating it but it's entirely possible to mix very old with very new and most drivers seem to allow it.
TLDR: 1. use VBOs, 2. use shaders. Just for learning, don't bother with an explicit version context.
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