@ahana ahana​  try this out:

%python
 
from pyspark.sql import functions as F
res = df.withColumn("start_date", F.to_date("start", "mm/dd/yyyy")).withColumn("end_date", F.to_date("end", "mm/dd/yyyy")).withColumn("date_diff", F.datediff("end_date","start_date"))

It works: