You have to first obtain the Range object. Also, getCell() will not return the value of the cell but instead will return a Range object of the cell. So, use something on the lines of
function email() {
// Opens SS by its ID
var ss = SpreadsheetApp.openById("0AgJjDgtUl5KddE5rR01NSFcxYTRnUHBCQ0stTXNMenc");
// Get the name of this SS
var name = ss.getName(); // Not necessary
// Read cell 1,1 * Line below does't work *
// var data = Range.getCell(0, 0);
var sheet = ss.getSheetByName('Sheet1'); // or whatever is the name of the sheet
var range = sheet.getRange(1,1);
var data = range.getValue();
}
The hierarchy is Spreadsheet --> Sheet --> Range --> Cell.