How to find accuracy of K means or any other Clustering algorithm?

I am working on a project where I am using K-means Clustering algorithm. But I need to check the accuracy of K-means algorithm. Can anyone help me with this ?
I have heard of Silhouette Coefficient, so I am trying to use that for k-means algorithm, But I am not able to use Silhouette Coefficient properly. Please help me as soon as possible.
If you want more details about data set, please let me know.

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