How to learn and interact with Mathematics on the browser using GeoGebra?

-- Browse to
http://app.geogebra.org/
-- Click on the Algebra link
--  On the left input textfield, type the following and then hit the enter key:
---- c =1
---- m = 2
---- y=mx + c
-- Click on "Toolbar > Angle of two lines with alpha icon > Slope". Click on the line to view the slope in triangle form
-- Go to the slider, drag to the left or drag to the right to change the c or m values
-- Other than Algebra section, try other Mathematics sections like Geometry, Spreadsheet, CAS, 3D Graphics, and Probability

An example from the above steps:

 
References
-- Animation: Move a Point, https://www.geogebra.org/m/n5ddtD86
-- Draw two functions in one graph with restricted domains, https://www.geogebra.org/m/GXC4GVEE