GeoGebra Books (online)  Tutorial from GeoGebra Classroom 
Visualizing Functions with Mapping Diagrams: MEI 2019 https://ggbm.at/nycagc2d 
GeoGebra YouTubes 
Intro to GeoGebra (YouTube)  Introduction to Classroom (YouTube) (!!) 
Work/Spread sheets 
MDWorksheet Functions and Equations 
Spreadsheet
Template (Linear
Functions) Spreadsheet Template (Quadratic Functions) 
Sections from MD from A B to C and DE (Drafts)  Visualizing
Functions: An Overview References 
Linear
Functions (LF) Quadratic Functions(QF) 
Flashman YouTube Videos 
Using Mapping Diagrams to Visualize Linear Functions (10 Minutes)Solving Linear Equations Visualized with Mapping Diagrams.

Using Mapping Diagrams to Understand Functions 
Mapping Diagram Sheets  Mapping
Diagram blanks (2 axis diagrams) 
Mapping
Diagram blanks (2 and 3 axes) 