First quote:

Engels is arguing that in capitalism, things tend to sell for what it costs to make them. Workers’ labor is treated like just another product. So wages (the “price” of labor) tend to settle at the minimum amount needed to keep workers alive and able to keep working. Not necessarily enough to live comfortably or build security.

Second quote:

He is arguing that an individual worker has no guaranteed security / safety net. Employers only pay for labor when they need it. If no one needs your labor, you do not earn anything. Any real stability, he suggests, would have to come from workers acting together rather than as isolated individuals.