Jeff,
When you have the Contact or Account record open for the person or the business look to the left side of the form and under Common you will see Opportunities. Click there and then in the new ribbon bar click on add new opportunity. It will automatically associate the new opportunity with the account or contact record. If you create the opportunity on the contact entity, it will rollup and be viewable on the account record that is parented by the contact.
If this answers your question, please make this post so we can close it out.