What are the single and double columns of a paper?

Occupy the width of one column and occupy the width of these two columns. A single column of paper occupies the width of one column, and the input content is filled from left to right, and automatically returns when it reaches the right boundary. Double columns occupy the width of these two columns, and the input content is filled from left to right, and automatically returns when it reaches the column spacing. When the first column is full, it will automatically enter the second column.