Why: In previous versions of SOQL, retrieving fields meant specifying all the names of all the fields you wanted to retrieve. Typically, this required first making an API call to describe the object to get the list of fields (or using the Object Manger) and then laboriously constructing a SOQL query to select all those fields. Further, such a query could exceed the query character limit for large complex queries that retrieve lots of data. The new FIELDS() function lets you select all the fields without knowing their names in advance. This eliminates the need for a round-trip to the server to prepare a SOQL statement, eliminates the need for research and a lot of typing, simplifies query statements, and makes it much easier to explore the shape of your objects.
How: Use FIELDS(ALL), FIELDS(STANDARD), or FIELDS(CUSTOM) in your SELECT statements. For more information, see FIELDS() in the SOQL and SOSL Reference.