Some Bootstrap grid system rules:

• Rows must be placed within a .container (fixed-width) or .container-fluid (full-width) for proper alignment and padding
• Use rows to create horizontal groups of columns
• Content should be placed within columns, and only columns may be immediate children of rows
• Predefined classes like .row and .col-sm-4 are available for quickly making grid layouts
• Columns create gutters (gaps between column content) via padding. That padding is offset in rows for the first and last column via negative margin on .rows
• Grid columns are created by specifying the number of 12 available columns you wish to span. For example, three equal columns would use three .col-sm-4