Unable to understand question

#1

question name is Count no of binary strings

#2

there cant be two consecutive ones in a string , and string consists of 0s and 1s only.
ex n=4
0000, 0010, 0100, 1001, 101,0001, 0101,1000

here you can see that these are made only of 0s and 1s and there are no two 1s together .

#3

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