Well, I'm not sure if this is just me, but I sometimes mistake conjunctions and preposition. Though, this course, somehow, help me to have a more clear understanding of these two part of speech. Wherein, conjunctions only joins or connect words, sentences, and phrases. Meanwhile, Prepositions shows the relationship between a noun and another word. For an example,
[CONJUNCTIONS]
"I wanted to go on a trip, but i feel sick."
[PREPOSITION]
"The trip is on Bali."