A deal is nothing but an activity that you undertake with the customer or contact. Whenever a contact visits your store and expresses a need of his, which could be as big as rennovating his entire house or as small as buying a bedsheet, both of these could be a deal for you.

Broadly speaking you create an activity or deal when you believe that there it is going to take you multiple interactions with the customer to close this activity. 

You can have various interactions with the customer during a deal which could vary from, shortlisting products, planning visits, taking measurements, collecting payments, taking notes and reminders and many more activities.

On the customer dashboard you can create a deal / activity by clicking on the + sign

You can enter the basic details of an activity like Deal Name and Deal Amount and start entering other interaction or digitization points against the activity