The Communication Logs helps you to keep track of all communication (incoming and outgoing) that you make between you and your sellers. It's also a shortcut to easily access the calls, emails and SMS related to the seller. Also, for the calls, you have the option to quickly listen to the voicemail or the recording of the conversation.
All Communications related to the Seller Leads will have a link to click on in the activity section and they can also be separately tracked in the Communications app.
Basically for each text, call and email a new Communication item will be created in the Communications app and linked inside the Seller Leads app.