Indeed, as the guys said before, there are 2 different sounds: "en" and "in". It's difficult for most of the foreigners to distinguish them. To help you, have a look at this website, you can listen to the different sounds: http://www.languageguide.org/french/grammar/pronunciation/ You can also use Forvo to search the pronunciation of each word: https://fr.forvo.com/

Vent et vend, oui, se prononcent de la même manière. "Vingt", "vin", c'est différent, totalement différent. Le son est le même que pour "pain", "main". Peut-être pourrais tu utiliser Google Translate et sa fonction sonore pour écouter la différence.

You have 2 different nasal vowels here. vin & vingt sound the same. vend & vent sound the same.