Salesforce has native functionality for handling basic organizational chores.  In Salesforce these are all types of 'activities"

Tasks - are Salesforce's name for "To Do" items.  You can create a task and associate it with any record, set due dates for it, and manage it through completion.  Great for reminding yourself of work you need to do related to that record or contact.

Events - Salesforce has its own native calendar, and appointments on that calendar (if you choose to use them), are called Events.  Whether or not you have a use for Salesforce events is up to you - and many people use Outlook or Google Calendar and don't want to duplicate this in Salesforce.  (Note:  There are integrations available in Salesforce to synch your Salesforce events with outlook or Google Calendar.  So if you want to use SF events in conjunction with your current calendar solution, you can do so.

Email - Salesforce makes it easy to send an email to a contact directly in Salesforce.  This can be handier than using your email client to send an email, because you can create and save email templates (for frequently used communIcations), easily merge in fields from your Salesforce data, and best of all, Salesforce keeps track of the email you sent as a related item to the contact record you sent it from.