The columns are containers with different widths, responsive and based on the 12-grid system of Bootstrap. You can change the column width by click on top right button . The columns are the main container of every content and are grouped into the rows. You must add the correct number of column to reach the full width of a row, a row is full when the sum of inner columns reach 12 (100%). For example if you insert 3 columns of with 4 (33.3%) you fill one row: 4 + 4 + 4 = 12, this is another way to write: 33.3 % + 33.3 % + 33.3% = 100%.