Questions about starting a business?

This isn’t something I’m betting my life on, it’s just an idea I’ve been toying with.
I’ve been reading about teenagers who have been self-made millionaires and it seems most of them made an app or started their own businesses.

I’ve been thinking for awhile about a type of clothing line I’d like to create. I’m not a designer and I don’t have very much experience in design or sewing, but I’m a bit of a connoisseur for fashion and I always find it difficult to find things that fit my personality in a decent price range.

How does one go about starting a clothing line? Do you just pitch the idea and come up with a few drawings? If so who do you contact for that sort of thing?
And if you don’t have the means to make the clothing yourself, who do you/can you hire a person/factory to do it for you?

Again, I’m just entertaining the idea. I’m not prepared to try anything yet but I’ve never been a follower and I’ve always been amused by the idea of having my own business or magazine.