The command plt.subplots(figsize = (10, 10))
, indicates that you want to divide canvas and create the subplots on it.
For your current requirement, you could do something like –
ax = sns.barplot(x='Submission Date', y='Count Handled', data=df_cd)
ax2 = ax.twinx()
ax2.plot(ax.get_xticks(), df_cd.Rating)
Here, you are creating the barplot first and adding the line plot over it with the same x-axis.