when they say crypto's are "banned" in other countries outside USA what's that?
99% of the times it is called spreading FUD (fear uncertainty and doubt). because it usually is a lie.
When they say countries banned these bitcoins, what happens when you log into Binance or Coinbase from the banned countrY?
it depends on whether they have actually banned bitcoin or was it a lie and also what kind of "ban".
there are a lot of different cases. when it is a lie (FUD) then nothing happens.
when it is banks banning their users from using exchanges (like India) nothing happens, you can still continue using exchanges but you won't be able to transfer fiat with those banks, so you have to change banks.
in rare cases (like 2 or 3 countries) that the government has actually banned usage of bitcoin, going to exchanges and trading with bitcoin can have consequences depending on the laws of that particular country which you need to research case by case.
No access somehow? Why not use a
VPN and access exchanges that way?
or TOR browsers
that could work as long as those exchanges don't ask for any KYC stuff you can freely use VPN or TOR and connect and enjoy using them.