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You need a knife.
Beyond that, progressively smaller tools for progressively smaller jobs. A saw, followed by a hatchet, maybe a chisel/gouge, a straight knife, maybe hook knife, then sandpaper.
Work out how big your finished product will be, add 1cm, cut. Trace an outline, cut. Trace details, cut.
If you're not working at a bench, don't bother with chisels and palm knives. You can't secure the work well enough to use them effectively or safely.
