how would you say just 'many' (not 'very many')?
You would use a form of multus, multa, multum most likely.
Canis multa ossa colligit. -> The dog collects many bones.
Os (s) 'bone' and Ossa (pl) 'bones' are third declension nueter, and can be Nominative or Accusative forms. In this case, ossa is accusative plural.