This bistable circuit is also known as /S./R Latch (active low inputs.)

In normal operation the inputs should not be asserted (set low) simultaneously as that may lead to a metastable output.

When S is asserted the output, Q goes high.

When R is asserted the output, Q goes low.

When both S and R are not asserted Qs state does not change. (It remains high if it was high or low if it was low.)