how does frat rush really work?

I am a sophomore transfer for reference

I have heard that in order to get a bid to any relevant house you really need to dirty rush. I get that dirty rush is just going to their parties and unofficial events this semester (for a bid in the spring). So my questions are

- Am I already late to the game for dirty rush?
- How does one get invited to these events? scenario: lets say I have acquaintances in houses that I would be interested in rushing - what is the right way to approach them about dirty rush?