A beta reader is, essentially, someone who reads your work and offers input while it is in draft form.
Generally, they look for typos, grammatical errors, continuity issues, etc.
Please check the tutorial below on how to create plugins.
If you find Fire Capture useful and would like to support me in continuing development you're welcome to donate a small amount of your choice.
Starting with version v2.5 Fire Capture comes with a built-in plugin interface giving access to image data and the possibility for extending functionality.
in order to help improve and polish your work before its submitted to a publishing professional or made public.
A lot of beta readers will do more than check for typographical errors, however, and will extend their generosity and time by critiquing and commenting on plot issues, characterization, believability, overall feeling, etc.
Whatever they find that they feel could use improving.