Possessive adjectives su vs sus

• What does “su” mean?

  His or hers
• When would you use “su”

  Before a singular or uncountable noun
• What does “su hijo es alto” mean in Spanish?

  his/her son is tall
• What would you use to say his/ hers or its before a plural noun?

  Sus
• What does “sus hijas son bajas” mean in English?

  His/her daughters are short.