Travelers to Vietnam, for all purposes (tourism, business, study, visiting relatives, volunteering...) need to obtain a valid visa before travelling (except citizens of a number of countries that are exempt from visas to Viet Nam with certain conditions, please refer to this link https://vnembassy-bangkok.mofa.gov.vn/en-us/Consular%20Services/Specific%20procedures%20application%20forms/Pages/Visa.aspx ).
To apply for an e-visa please click this link: https://evisa.gov.vn/