The document discusses different types of adders used in digital circuits, including half adders, full adders, and ripple carry adders. A half adder adds two single binary digits and produces a sum and carry output. A full adder adds three binary digits and produces a sum and carry by using a combination of half adders and logic gates. A ripple carry adder is constructed by cascading multiple full adder blocks in series, where the carry output of one stage is fed into the next as the carry input.