explain the basic functionality of bootstrap please see details below

Please answer questions 1,2,4 and 5 to the best of your ability means the world to me. Give an application of Bootstrap. Write the HTML code to produce a layout of 2 rows, the first row containing 1 column with a width of 12, the second row (below the first row) containing 3 columns with a width of 3, 6, and 3, respectively.

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