Textual analysis is a process to analyze the system domain. It helps to identify the candidate classes in a problem statement.

From a problem statement, extract the word for candidate objects and add it as candidate class.

Candidate object can futher convert into class model for usage in other diagram (shared model).

For your own interest, please visit the following links:
Textual Analysis Tutorial

For other UML tutorial, please visit the following web site:
Use Case Diagram Tutorial
Sequence Diagram Tutorial
Activity Diagram
Collaboration Diagram
State Diagram
Class Diagram
Component Diagram
Deployment Diagram