I was making the first game though in private only my friend that I would give the link but when I start to submit it, it ask me to upload files and despite I been doing this I was stuck and unable to do.
How can I do this?

Files will fail to upload if they're too big (the limit is 20MB, I think), or the wrong type (for Quest games, you need to upload the published .quest file).

Does it give any kind of message to tell you what's wrong?