Any prospective student who seeks to pursue higher education in a foreign country must possess a student visa from that country. A student visa is issued to students who are enrolled at the qualified educational institution.
Since student visas are non-immigrant visas, the holder need not obtain citizenship and is valid for the duration of the course they are undertaking. Sometimes they also receive an added tenure where they can stay back in the country and seek a job.
Some countries will require a combination of visas. For example a student visa and a non-immigrant visa for a temporary stay or an immigrant visa for permanent residence along with a student visa. This is because most countries will issue student visas that will allow foreign students to attend school within their borders. However, in most cases, it is a requirement that the student is already enrolled at a post-secondary institution of higher learning.