https://i.ytimg.com/vi/U9jXOx7S32I/hqdefault.jpg
This tutorial shows the basics of making the lower body of a humanoid character. The tutorial shows how to make a pair of shorts but extending the legs is relatively straight forward (and will be covered in a future tutorial).
Key points –
You can use the subdivision surface modifier to make a low polygon count model.
You can use the mirror modifier, apply it when you want to work with both sides, then delete half and re-apply when you want to work with one side.
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