If you've written a formula that calculates cells in one row and you'd like to apply that formula for additional rows without manually pasting it for each cell, click into the cell with the formula, drag to highlight cells downward and choose Fill Down from the Calculate menu. Alternatively, you can drag to the right and select Fill Right from the Calculate menu. Cell references in the formula will be incremented by 1 automatically unless you indicate an absolute reference by preceding the cell reference with a $ symbol, e.g. $A$1.
The Fill commands also work for entering data (not just formulas) you want to repeat through a range of cells.
This is covered in Page 6-11 of the ClarisWorks 2.x User's Guide, Page 5-12 of the ClarisWorks 2.x Getting Started manual, and in the Online Help (look for "Cells: filling automatically" in the index.)