Une & Un
I need help. When do I use ''Une'' and when do I use ''Un''?
Others have described it very well. I will add that it is a great idea to say these out loud with the nouns they refer to as you study them. After studying French for years I still don't have every single one memorized so sometime have to go by what "sounds" right, what I heard in the exercises and what I have practices saying. There is no real rhyme or reason to what is masculine and what is feminine...at least nothing that you can apply to every word. So just start memorizing and listening and speaking.
Check out this link: https://www.france-pub.com/french/masculine-feminine.php for some information on gendered nouns in French. As far as knowing which words are which, try to learn the article along with the noun- i.e. don't just learn "garçon" for boy, learn "le garçon" the boy (or "un garçon": a boy). It's basically a matter of repetition until you know which gender a word is. This isn't the most natural thing for English speakers, but you'll get there! :)