To each business deal, you can add other Accounts and Contacts who are somehow involved in a particular business deal.
Here is an example for a better demonstration :)
I have a "Parachute jump" deal. I need to keep track of which members and pilots have been involved in this deal. So I simply create a relation to the business deal for them.
And how to do this?
Click the Add relation button in the business deal detail.
Select if you want to add an Account or a Contact.
Type in the name of a person you want to add or click the double arrows at the end of the field and search for the person in the Contact list.
You must also fill in the Note field where you describe the relation which this person has to the business deal. Confirm by clicking Save.
If you need to edit a relation description, click the pencil icon. In case you want to remove a relation completely, click the cross.
To add another relation, click the Add button and select if you want to add an Account or a Contact.
Click the contact's name to enter the record detail of this person. The relation to a deal can be found in the History tab. (The same procedure applies for Accounts).
You can easily find out which people were involved in which deals thanks to the relations.