Cell formula are similar to popular spreasheet. Use a letter for the column, a number for the row, the $ sign before a row/column indicates an absolute reference, the = sign at the beginning of the cell indicates a formula. For an area of cells, write the reference to the up, left cell, then : then the reference to the down right cell for example =mean(A1:B4) will compute the mean of the cells rows 1 to 4, columns A and B.
Using the table and tableseq of the Edit->Spreadsheet menu, it is easy to make table values of functions or sequences.
You can select a submatrix with the mouse and copy it elsewhere. It is also possible to extract more complex submatrices using the input area in the mode button bar, for example B3:B7,D,E. The menu bar in the middle may be used to do statistics on the selection.