How to handle Strings in Statistics and Machine Learning(Predictive Analytics) as my data set has many alphabetic strings in various columns.

Trying to implement a Predictive Analytics model but I'm unable to access/handle most of the columns in my data set because they are strings. I have used Classification Learner App but when i'm selecting data set from the work space i'm only able to see all the columns with numerical values but not the columns with string or date or enum. And how to build a Random Forest Algorithm for predictive analytics.