If you entered the US legally and marry a US citizen, you can usually apply for adjustment of status inside the US. But you need to be careful not to misrepresent your intent when entering on a tourist visa.

Some people leave and apply through consular processing, but that can take longer. Adjustment of status is often faster if you qualify.

Talk to an immigration attorney before filing. Intent issues and timing are important; a professional can help make sure you don’t accidentally create a problem with your entry status.