The logic symbols shown here are logically equivalent to:

The “bubble (O)” at input side represents negated values.

$\begin{array}{l}\text{ fig a: }Y=\overline{A}+\overline{B}\\ =\overline{A\cdot B} \left(NAND\right)\\ \text{ Fig b: }Y=\overline{A}\cdot \overline{B}\\ =\overline{A+B} \left(NOR\right)\end{array}$