Menu display problems

When I choose my menu as the primary menu, it no longer displays horizontally as a drop-down menu. Instead, it bunches up terribly, and you can’t click on anything. However, if I uncheck the menu as primary, then the site displays my pages in a horizontal bar in the order they’re in on my page dashboard. That’s the look that I want, but if I leave it that way, I can’t customize the links for each of the header items. How do I remedy this? I’d like to make my menu a horizontal drop-down menu that doesn’t distort.

Disclaimer: I have no coding experience, so if there’s a way to fix this without code, I’d prefer that.