The value of a cell, from one sheet to another sheet (in the same document)

The value of a cell, from one sheet to another sheet (in the same document)

Hi everybody!
I am from Spain, so it's quite difficult to explain the question I have, but I will try it and I hope you will understand my problem, and, hopefully, you can give me a solution.

I have created one document (spreadsheet) with different sheets in the same document.
And I just want to put in one cell of sheet 4, different values of sheets 1, 2 and 3, so, to makes balances.
I am trying, like in Excel, to put "=", and I go to the sheet, click the cel, and push Intro...and this should work, but it doesn't.

I hope you can help me.

Thank you in advances.
My email is bilbao@catalweb.net