Apex is a very strongly typed object-oriented, on-demand programming language. It is compiled, stored, and run entirely on the Force.com platform (multi-tenant environment and is very controlled in its invocations and limits as it’s running on cloud).

Note : It’s a case insensitive language.

• Apex syntax looks mostly like a Java programming language.
• Apex allows developers to write business logic to the record save process.
• Apex has built in support for unit test creation and its execution.

Apex provided build in support for followings:

• Data Manipulation language(DML) calls to insert, update, and delete record.
• Inline SOSL or SOQL statements for retrieving records from sObjects.
• Looping control structures that help with bulky processing.
• A record locking syntax that prevents records being conflicts.
• Custom public API calls.
• Send and receive an email.
• Web services(REST/SOAP) request/response integrations.
• Warnings and errors to prevent sObjects referenced by Apex from being modified.

As a language apex is Integrated, Very easy to use, Data focused, Rigorous, Hosted, Multi-Tenant aware, automatically upgradable in nature, easy to test and versioned.

When developers write & save their code in a platform, which is compiled on force.com platform and stored in the form of metadata in Salesforce servers then end users can send requests from UI & retrieve results from Salesforce servers.

Below are few capabilities of Apex

When we can use Apex programming?

Apex should be used as a solution when:

• You need to write complex business logic to rows of data being saved by any means.
• You need to create additional web services API functionality for exposing logic either within Salesforce or to outside of Salesforce.
• You need to call out to an external Web service and process the results.
• You need to manage incoming or outgoing emails in ways more complex than the declarative functionality.
• Apex triggers execute no matter how the triggering data is being saved.
• Apex executes regardless of whether the action originates in the user interface, through AJAX toolkit, or from web services API.
• If you only want the code to execute through UI, consider making a visualforce page and controller.

Difference b/w traditional programming & Apex programming

Traditional code is fully flexible, and can tell the system to do anything as per the requirement.
Apex is a governed language, can only do what the system allows.