5.1First: Salesforce is basically an object database

Think:

Salesforce org
   │
   ├── Account
   ├── Contact
   ├── Opportunity
   ├── Case
   ├── Lead
   ├── User
   └── Custom_Object__c

Each object contains records.

Conceptually:

Account
--------------------------------
Id
Name
Phone
BillingCity
Industry
External_Customer_ID__c

Very roughly, if you're coming from SQL:

Salesforce Object ≈ table
Salesforce Record ≈ row
Salesforce Field  ≈ column

But don't push the analogy too far because Salesforce relationships and APIs behave differently.