Do

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Do[expr, {max}]

evaluates expr max times.

Do[expr, {i, max}]

evaluates expr max times, substituting i in expr with values from 1 to
max.

Do[expr, {i, min, max}]

starts with i = max.

Do[expr, {i, min, max, step}]

uses a step size of step.

Do[expr, {i, {$i_1$, $i_2$, ...}}]

uses values $i_1$, $i_2$, ... for i.

Do[expr, {i, $i_{min}$, $i_{max}$}, {j, $j_{min}$, $j_{max}$}, ...]

evaluates expr for each j from $j_{min}$ to $j_{max}$, for each i from $i_{min}$
to $i_{max}$, etc.

You can use Break[] and Continue[] inside Do:

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