Check out example codes for "how to make checkbox checked in html". It will help you in understanding the concepts better.

Code Example 1

<input type="checkbox" name="vehicle3" value="Boat" checked>

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Code Example 2

<!-- Add checked tag  -->
<input type="checkbox" name="vehicle3" value="Boat" checked>

Code Example 3

<input type="checkbox" checked={props.completed} /> 

#for props completed is true/false , hence if completed is false then checkbox will not be clicked .
# if the checkbox is true it will be will be checked

Code Example 4

<input type="checkbox" name="vehicle1" value="Bike">

The checkbox value is 'Bike'.

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