Build a prototype/mvp/alpha/demo product. Something. Anything. Then depending on the type of startup, there are so many ways to get started. If you live in a big city, go to tech meetups and start gathering contacts who will help you get to angel investors. Or apply to incubator programs like YCombinator (there way more of these than you think). Regardless of the avenue, i repeat, work on your product and your pitch. Neither come easy.