Irw wrote:when i enter the usa, what happenes if they deny my access?
Depends on why you have been denied entry. You could be put on the next flight back home or at worst locked up overnight in jail pending your flight being organised - the latter is usually for expedited removal on grounds of fraud/ misrepresentation with a 5 year or lifetime ban as the case may be (misrepresentation of US citizenship) from the US and no scope for judicial review.
Irw wrote:do they stamp my passport with something?
sure they do - your visa will be cancelled/ invalidated and relevant codes of the INA (Immigration Act) stamped thereon.
Irw wrote:do they leave a bad thing under my name for other countries to see when my passport gets scanned?
The stamping above is an obvious give away of your US entry refusal. However your fingerprints and photo will be taken under VISIT scheme and details of the refusal will be added to the relevant immigration IT system. It may be some of this information is shared with other countries - as you would expect governments don't exactly give relevant details.
What is the purpose of your trip to the US and why do you expect to be refused entry?