I have seen a similar questions here but i want to know is the idea of the next proof is right
We know that $S^n$ has a CW structure given by $1$ $0$-cells $e^0_{\alpha}$ and $1$ $n$-cell $e^n_{\alpha}$ and the same for $S^m$ has a CW structure given by $1$ $0$-cells $e^0_{\beta}$ and $1$ $m$-cell $e^m_{\beta}$
and then $S^n \times S^m$ has the next cells $e^0_{\alpha} \times e^0_{\beta}$, $e^n_{\alpha} \times e^0_{\beta}$ $e^n_{\alpha} \times e^m_{\beta}$ and $e^0_{\alpha} \times e^m_{\beta}$
but the smash product is defined to be $S^n \times S^m /S^n \vee S^m$ and then $e^0_{\alpha} \times e^0_{\beta}$, $e^n_{\alpha} \times e^0_{\beta}$ and $e^0_{\alpha} \times e^m_{\beta}$ are "colapsed" to one point so we have a point and a $e^n_{\alpha} \times e^m_{\beta}$ cell and then is homeomorphic to $S^{n+m}$