KMeans clustering

2. Unsupervised learning is a type of algorithm that learns patterns from unlabeled data.
Unsupervised Learning
Clustering is a type of unsupervised learning.
K Means Clustering
K Means clustering grouping the samples based on Euclidean distance.

3. How to decide the number of clusters?

7.  Clustering process will initiate random centroids (number of centroids will be equal to
number of clusters).
 Based on the Euclidean distance between data points and each centroids, the centroid
positions and the data belongs to each centroids adjust.
 This process continuous and finally divide the samples into given number of clusters.