It sounds as though you are struggling on this assignment but have made a good start in understanding why you are having issues with it.
The first issue seems to be understanding Le Morte d'Arthur. This text was first published by Caxton in 1485 after the death of its author Thomas Malory. It is written in Early Modern English which is comprehensible by speakers of modern English but requires some concentration. There are two ways you can help yourself understand the book. The first might be reading a modernized version such as that by Peter Ackroyd or the full eNotes summary before returning to tackle the original so that you have a sense of the overall plot. Next, you should set yourself a goal of reading one chapter at a time with no distractions (phone off, music off, TV off) and taking notes and highlighting as you read. You might also make index cards for each major character, and as you read, whenever something important happens to a major character such as Merlin or Arthur or Mordred, adding a note to the card for that character.
The association of Kennedy's presidency with Camelot had its origin in a interview between Mrs. Jacqueline Kennedy and a journalist for Life magazine shortly after Kennedy's assassination, in which she applied a quotation from the popular Broadway musical Camelot to her husband's presidency saying:
Don’t ever let it be forgot, that once there was a spot,
for one brief shining moment that was Camelot.
In your essay, you should outline points of comparison between Kennedy's presidency and Arthur's kingship. The first parallel is that Kennedy was both a charismatic and highly polarizing figure who won the popular vote by less than one percent, just as Arthur was also not universally accepted. Also, Kennedy was youthful and assassinated in the prime of his life, like Arthur.
Next, the Round Table was intended as a gathering of the greatest knights in the world. Kennedy famously gathered around him many distinguished thinkers and intellectuals, the "best and the brightest" of his generation; you could draw parallels between the Kennedy Cabinet and the Round Table.
You might also want to introduce another parallel between Kennedy and Arthur, namely that both were rather notorious philanderers, with Arthur's downfall being caused by his illegitimate son and Kennedy's staff struggling to keep his many affairs away from the press.