Easyyyy...just kiddin, first you should start making a blockout to get the proportions, when that is ready, start going up one time add medium details....high details....and dont forget to model them like in real life / separated objects.
Think of it as a narrow square up for the calf and a boxier square for the lower half, then just start carving away and make the forms rounder, to match the appearance, make sure you get the anatomy of each piece right
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https://www.youtube.com/watch?v=xtGEghClPsw