Quotes vs Invoices vs Sales Orders

Quotes vs Invoices vs Sales Orders

We have the need to create either quotes, invoices or sales orders for services we provide to clients for our sales team to present to them.  However, we are confused in the purpose of each and which we should choose.  Could someone explain the difference in them?

Also, with these, we will have setup costs for our clients and then fixed monthly costs.  For instance, we have services that are one-time services at $997 and then we have others that are monthly only ($250 per month).  In addition, we have some that have both fees - $997 setup upfront and $250 per month.  What is the best (quote, invoice or sales order) to handle this and how have others handled it?