setValue()

SpreadsheetApp.getActive().getRange("A1").setValue('abc');

var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getSheets()[0];

// The size of the two-dimensional array must match the size of the range.
var values = [
  [ "2.000", "1,000,000", "$2.99" ]
];

var range = sheet.getRange("A1:C1");
range.setValues(values);