punctuation - How are bracket ellipsis [...] used in quotations?

I see this type of syntax often, but I do not know how, when or where they should be used.

"It is the case that [...] the inconvenience is altogether imaginary."

Is it okay to use if I need to insert a quotation into an essay, but the quote is long and I want to omit the irrelevant parts? Am I allowed to use the syntax multiple times per quotation ?