Types of indexes:

Clustered: It sorts and stores the data row of the table or view in order based on the index key.

Non clustered: it can be defined on a table or view with clustered index or on a heap. Each row contains the key and row locator.

Unique: ensures that the index key is unique

Spatial: These indexes are usually used for spatial objects of geometry

Filtered: It is an optimized non clustered index used for covering queries of well defined data