Opportunities are qualified leads, each individual recruiter may qualify a lead at a different stage it could be before or after contact has been made with the key decision maker. Some recruiters may qualify the lead as soon as they’ve been given the decision makers details, others may only qualify them after having an in-depth discussion about their requirements or when they’ve issued a quote.
When converting the lead to an opportunity you can choose to add the person to your contacts or you can do this later when you have gained a job from them.
Opportunities are then converted into a job when the deal has been closed and your company has been employed to search for the candidate. In the opportunities tab, you can add the deal value, win probability, start date, and a description as well as other useful information.