Two-column mode lets you conveniently edit two side-by-side columns of text. It uses two side-by-side windows, each showing its own buffer. There are three ways to enter two-column mode:

=F2 2= or C-x 6 2

Enter two-column mode with the current buffer on the left, and on the right, a buffer whose name is based on the current buffer's name (2C-two-columns). If the right-hand buffer doesn't already exist, it starts out empty; the current buffer's contents are not changed. This command is appropriate when the current buffer is empty or contains just one column and you want to add another column.

=F2 s= or C-x 6 s

Split the current buffer, which contains two-column text, into two buffers, and display them side by side (2C-split). The current buffer becomes the left-hand buffer, but the text in the right-hand column is moved into the right-hand buffer. The current column specifies the split point. Splitting starts with the current line and continues to the end of the buffer. This command is appropriate when you have a buffer that already contains two-column text, and you wish to separate the columns temporarily.

=F2 b buffer RET=, C-x 6 b /buffer/ =RET=

Enter two-column mode using the current buffer as the left-hand buffer, and using buffer buffer as the right-hand buffer (2C-associate-buffer).

=F2 s= or C-x 6 s looks for a column separator, which is a string that appears on each line between the two columns. You can specify the width of the separator with a numeric argument to =F2 s=; that many characters, before point, constitute the separator string. By default, the width is 1, so the column separator is the character before point. When a line has the separator at the proper place, =F2 s= puts the text after the separator into the right-hand buffer, and deletes the separator. Lines that don't have the column separator at the proper place remain unsplit; they stay in the left-hand buffer, and the right-hand buffer gets an empty line to correspond. (This is the way to write a line that spans both columns while in two-column mode: write it in the left-hand buffer, and put an empty line in the right-hand buffer.) The command =F2 RET= or C-x 6 =RET= (2C-newline) inserts a newline in each of the two buffers at corresponding positions. This is the easiest way to add a new line to the two-column text while editing it in split buffers. When you have edited both buffers as you wish, merge them with =F2 1= or C-x 6 1 (2C-merge). This copies the text from the right-hand buffer as a second column in the other buffer. To go back to two-column editing, use =F2 s=. Use =F2 d= or C-x 6 d to dissociate the two buffers, leaving each as it stands (2C-dissociate). If the other buffer, the one not current when you type =F2 d=, is empty, =F2 d= kills it.