Corporations are entities that exist as contracts between people. The theory is that the speech of a corporation is thus the speech of the people involved in the contract.

No one is protected by the First Amendment. The government is forbidden to do things. "Congress shall make no law abridging the freedom of..." several things, including freedom of speech.

The idea that corporations were given First Amendment rights by a recent Supreme Court decision that made them people is very frustrating to me. Corporations were deemed "people" in 1882, in San Mateo County v. Southern Pacific Rail Road, but it doesn't matter even slightly what they are with regards to the First Amendment, which doesn't specify who is speaking. Whether you're a citizen, noncitizen, undocumented immigrant, visitor, or soulless capitalist entity, if you can speak, Congress shall make no law.