It seems like レ点 is used more than レ by itself, but I imagine you could use it the same as チェックマーク.
Like:
空白に（チェック・チェックマーク・レ点・レ）を入れてください
Please put a check in the blank space.
At least, that would be in theory. Like I said, I don't think レ is used this way on its own much in practice. But it does exist.
It's related to the subject of Kanbun (漢文) in classical literature, which are chinese works of literature written in chinese. Highschool students in Japan have to learn how to read them but they're not gonna learn chinese lol so the レ (and other marker) is used to help them read those chinese sentences/Turning those chinese sentence into semi-normal japanese sentence.
Example: Chinese: 人不学... (ren bu xue)＝ People (who) dont study....
=> here they would use the レ to mark the sentence like this: 人不(レ)学 to say "reverse the order of 2 adjacent word"
-> turning that sentence into: 人学不 ー＞ simply turn 不 into negative form of the verb in front of it then they will read 人が学ばない
*note that these exercise usually use vertical orientation written form so they would simply add a small レ mark on the side between the 2 letters.
more example for you: just google "漢文レ点”
How is this used in a sentence?
レ
Some examples will help