# Is it OK to post images/text from a textbook?

I'm self studying a textbook and sometimes I do not understand the explanation the author is trying to give for a concept. Is it OK for me to write out what the textbook says verbatim and/or take an actual image from the page and post it on SE? I'm not going to post an entire page, just excerpts.

But "I understand the definition of group and subgroup. But in the argument reproduced above it says 'the subgroup $H$ is normal' and I do not know what this means or how it is relevant to the argument." is an alright question.