I'm a musician myself, so I know what it's like to feel like there-be-monsters guarding the gates. However, I don't accept unsolicited submissions. Wanna get me to listen your music? I host a monthly listening session through Sync Music for a Change that you can submit a song to, if you want a chance to show me what you do. And in the meantime, if you're new to sync licensing you can learn how it all works here.
Here are some helpful links:
Music licensing is a competitive business. I recommend joining as many FB groups around sync as possible in order to understand the business, the etiquette of reaching out, find out what agents other people are using, learning about music licensing conferences etc. Other musicians in these groups are your best resource!