[researching]

I am a student and new at studying the differences in Bible translations. My assignment for this week is to start studying the difference between translations and find out why they are different. I did not know there were any major differences until I started my research.
I read that “the NKJV translators departed from the original KJV and its underlying Greek text, the Textus Receptus, in favor of the very same wording found in versions translated from corrupted Greek texts.”
Why are the other texts considered corrupt? Do they also use the Textus Receptus? Thanks in advance for any help.