The ALU can be used both for signed and unsigned addition. Unsigned addition is slightly simpler, because each bit represents a numerical value (a power of two), so the result is immediately ready to be interpreted as a binary number once addition is performed. Subtraction is more difficult to perform, as adding a Two's complement doesn't work, but an ALU can still implement the circuitry necessary for it. As a reminder, unsigned and signed addition are the same technical process yielding the same bit pattern that may be interpreted in different ways.
The ALU can be used both for signed and unsigned addition. Unsigned addition is slightly simpler, because each bit represents a numerical value (a power of two), so the result is immediately ready to be interpreted as a binary number once addition is performed. Subtraction is more difficult to perform, as adding a Two's complement doesn't work, but an ALU can still implement the circuitry necessary for it. As a reminder, unsigned and signed addition are the same technical process yielding the same bit pattern that may be interpreted in different ways.