Can an ordinary person speak in the usa Congress,?

Yes. Anyone in the world can speak on the floor of the US Congress BUT you have to be invited to speak by the Speaker of the House (meaning you'd need to be recommended by a member of Congress) AND the Speaker needs to add you to the agenda.

In reality, I cannot think of a situation where an "ordinary" person would be afforded the opportunity.

Normally an ordinary person can speak in the USA to their Congressman and the Congressman can speak in front of congress.

But you better bring a hefty campaign donation.

Now if you don't have a hefty campaign donation than the ordinary person speaks to a lobbying organization that does have hefty campaign donations.

Like the National Right to Life Committee, or NARAL Pro-Choice America - for abortion positions
The John Birch Society
Americans for Prosperity
American Civil Liberties Union - ACLU
National Rifle Association

You can speak to your congressman.

That is why we elect the Congress is to speak for us. And to say that they can't vote just shows you are clueless and need to go back to civics classes.

Not without being invited. "If no,than no congressman can vote." I have yet to see that limitation in the constitution. Perhaps you can point it out to us.