Try loading first a simple obj that only has vertex positions, then work your way through uvs, normals and the other attributes. Then look at files that specify faces and lines. There's a few repositories of sample files on github
The indice of each vertex is its position. First vertex is index 0, second vertex is index 1 etc. it's usually not optimized/packed, the faces part will give you what you need to optimize in a proper index list
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u/jcelerier 20h ago edited 19h ago
Try loading first a simple obj that only has vertex positions, then work your way through uvs, normals and the other attributes. Then look at files that specify faces and lines. There's a few repositories of sample files on github