Your initial state is two qubits in state 0, i.e. $|00\rangle = |0\rangle_{\#1}|0\rangle_{\#0} = |0\rangle_{\#1} \otimes |0\rangle_{\#0}$ (subscript indicates qubit1 and qubit0.)
Now, you are applying $Y$ to your qubit1, and you are doing nothing to qubit0. Doing nothing is equivalent to multiplying by the identity matrix. So your operation is as follows.
$$
|00\rangle \rightarrow Y_{\#1} \otimes I_{\#0}|00\rangle
$$
Evaluating this,
$
\begin{align}
Y \otimes I|00\rangle &= (Y \otimes I)(|0\rangle_{\#1}\otimes|0\rangle_{\#0})\\
&= Y|0\rangle_{\#1} \otimes I|0\rangle_{\#0} \\
&= i|1\rangle_{\#1} \otimes |0\rangle_{\#0} \\
& = i |10\rangle
\end{align}
$
Try following these equations by multiplying explicitly using matrices and vectors; where
$$Y = \begin{bmatrix}
0 & -i\\
i & 0
\end{bmatrix} ;|0\rangle = \begin{bmatrix}
1 \\
0
\end{bmatrix}
$$