Collecting TextEntry data

I have a variable "TextEntry" field set up for learners to provide a written answer. I would like to be able to trig a Javascript when learners write inside the TextEntry field.

The final goal would be to collect the learner's answers. 

Is anyone willing to help me with step by step about how to do this?  I don't need the Javascript, just the way to trig the process

I would really really appreciate it!!  :-)