The most common and most likely answer to this crossword clue is the 10 letter word GLOSSARIES
I've seen this crossword clue in The Times
G
L
O
S
S
A
R
I
E
S
Buddy explains!
The straight part
We know that "They help people understand words" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they help people understand words = glossaries.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GLOSSARIES mean?
GLOSSARIES noun- A list of terms in a particular domain of knowledge with their definitions.