Does the word "замок" have several meanings?
This word has several meanings depending on which syllable you choose to stress. If you say замОк, it means "lock". If you pronounce it as зАмок, its meaning will change to castle.
Can I use le Passé Simple when speaking about my past?
You can't. Le Passé Simple isn't used in spoken French, it's primarily used in literature. You should use le Passé Composé, l'Imparfait or le Passé Récent.
Is there a difference between the meaning of the words timid, prudent and cowardly?
These words differ in connotation. The word timid is a neutral one, cowardly bears negative meaning and the word prudent gives a positive evaluation of a person who is careful in decision-making.