How do you use the Opportunity and the Quoatation modules differently?

How do you use the Opportunity and the Quoatation modules differently?

This may seem like a stupid question, but I would really like to know how do you use the "Opportunities" and the "Quoation" modules.

I feel like they're the same.  And the Quoatation module actually has more useful and specific fields like the products and their values, but in the Opportunity you only have a single field for the Amount Value.  

I'm new to CRM and I don't understand the need for "Opportunities" anymore.  But the "Sales Funnel" is useful only in Opportunities and NOT in Quoatations where I find it more logical.

So, How do you use the Opportunity and the Quoatation modules differently?