I just started learning Mathematics, and was given a notebook. There is a cell with 'text' format, but there is one line that is a command, so I change that line into 'input' format, and press 'Shift+Enter', but still couldn't evaluate that line.
And I found that within the whole cell, I cannot click anywhere to display a 'horizontal line' for which I can start typing input. Also, the cell bracket has two horizontal lines on the top, so does it mean that I cannot evaluate any lines in such a cell? And have to start a new cell?
Any help is appreciated!