I am struggling with what they mean. Please explain
To learn about basic polynomial terms (such as "term", "monomial", "binomial", etc), try some online lessons to supplement the information in your textbook and your class notes.
There are also loads of online lessons available for completing the square. Study at least two lessons, and make sure you take the time to work through all of the examples, so that you're sure you're understanding the process.
Have fun!