You contact 10-20 suppliers, with relevant questions (lots of suppliers email templates available, Google them); ask for samples, evaluate the product; if you’re happy make a bulk order.

Many options available, they all have their pros and cons.
Ship freight is cheaper but it takes a lot longer + there are all the import/duty procedures involved. It’s better for larger shipments.
Air is more convenient though more expensive.
As a newbie I’d recommend that you go with air express initially. Until you build up to large orders and have more experience to deal with customs.

DHL takes care of it for you.