The visa issuance and expiration dates are mentioned on your visa. Your visa is valid from the date of the visa issuance to the visa expiration date. You can travel as long as your visa is valid. Depending on your citizenship, you may have a single entry, a multiple entry or an unlimited entry visa. This defines the number of times you can enter the foreign country.
Different countries have different passport validity requirements. Mostly, your passport needs to be valid for at least six months beyond the length of your trip. It is, therefore, a good idea to renew your passport nine months before it expires.
Individuals holding a non-immigrant visa should avoid remaining in a foreign country beyond their visa expiry date. If they desire to stay longer than this, they need to file for an extension or for a change of status.
If you wish you prolong your stay beyond the expiration date of your visa, renew your visa immediately. You may use the accelerated services of the State Department to shorten the processing time of renewal.
If you stay in the US beyond the authorized time, you will be considered out-of-status by the Department of Homeland Security. This is considered a violation of US immigration laws and exposes you to legal proceedings. You may be deported and may even become ineligible for obtaining a US visa in the future. For more details, visit this website.