The necessity and the procedure to obtain a visa vary a lot. It depends on the country of destination and the nationality of the traveler.
Therefore, I think it is easier for me to give you such information when I post about each country.
What I can advance for now is that the citizens from the country members of the MERSOSUR (Brazil, Argentina, Uruguay and Paraguay) don’t need a visa to enter in any of the country members of the treaty.
And for those willing to come to Brazil, I advice you to visit the official governamental website: https://scedv.serpro.gov.br/frscedv/indexIdiomaIngles.jsp?lang=eng to check if you need a visa to enter the country.
The link I provided is in English, but they also have it in French, German and Spanish.
There you will find when the visa is required, which requirements you need to fulfill in order to get one, the different types of visa and its request form.
In case you have any doubts or are facing difficulties to access the website, please do let me know through the comments section or here.
And if you need specific information about a destination that it was not yet posted, ask me in the comments section or here.