Mesh, Vertices and Indices

I’d like to suggest better documentation or a tutorial for working with meshes, polygons, vertices etc… I’m far from a 3D graphics and geometry expert but I think I understand enough to write some code to create or manipulate models and meshes. Trouble is I have a hard time understanding the part of the API that deals with all of that.

I’m used to mesh data structures containing an array of vertices and an array of triangles. So basically, for a simple plane with two triangles, the array of vertices ([x,y,z…]) would look like [ 1, 1, 0, -1, 1, 0, -1, -1, 0, 1, -1, 0 ] and the array containing triangles ([VertA,VertB,VertC…]) would look like [ 0, 1, 2, 0, 2, 3 ]. How do I go about extracting and modifying this information from an existing mesh and how do I create a new mesh (thru code, not a fbx, obj or json file) with this kind of information?

Thanks for your help.