You can schedule follow up with leads by clicking the purple arrow beside the lead's information:
Once selected, you will find the option, "Schedule followup." Then it will prompt you to enter in the date and time you wish to follow up, and you can also enter in notes pertaining to the follow up. If you choose "Add to Google Calendar," it will ask you to select which Google Calendar to save the appointment to, and by doing so, you will see the option to set yourself a reminder so many minutes prior to the followup scheduled. That reminder will be internally for you. It will be a popup alert banner so you are properly notified.
If you do not already have a Google Calendar integration, you can connect one by going to the Google Calendar page located in the navigation bar on Ringy.