Contacts
What is Contacts?
Contacts in Salesforce store an individual's demographic information, such as phone numbers and email addresses, and are linked to accounts.
If a contact is not linked to an account then it is a private
contact and only viewable by the contact owner or Salesforce administrator. One contact = one person.
Create a Contact
To create a new contact, select the Contacts
tab and click on the New
button. This will open a page where you can enter the details for the new contact.
Complete all mandatory and any additional optional fields if necessary, then click the 'Save' button

Other way to create a contact while creating an account
You might already know. if not click here
Activities:
The activities functionality is common and is exactly the same as the Accounts functionality. If you're not sure how to use it, click here for more information.