This appears to be a Joro spider weaving a web in the backyard. It seems the spiders came from East Asia, but have been more and more common in the United States.
The Joro spider (Trichonephila clavata) is not considered dangerous or highly poisonous to humans. While it is venomous, as are most spiders, its venom is primarily used to subdue small prey like insects. In the rare instance of a bite, symptoms are typically mild, resembling a bee sting, with localized pain, redness, or swelling. Serious allergic reactions are uncommon, but like any spider bite, they could occur in sensitive individuals.
In general, these spiders are more of a nuisance than a threat to humans and play an important role in controlling insect populations. If you encounter one, it’s best to leave it alone.