Matrix dialog box
Insert > Multimedia > Equation… – click 
then click 
Use this dialog box to specify settings for an arbitrary-size matrix in a mathematical formula.
Rows/Columns
Enter the number of rows and columns for the matrix.
Vertical Align
Specify how to align the matrix vertically with respect to other symbols on the same line. “Top” means align the top of the matrix with the rest of the line.
Horizontal Align
You can choose one column in which the symbols will be aligned horizontally a certain way. Use the column control to specify the column, and then select Left, Center, or Right. (All other columns will be center-aligned.)