What happens after paying the immigrant fee?

After paying the immigrant fee, what is the next step in the immigration process? Does the payment confirm my eligibility for permanent residency or is there more to be done? Are there any additional forms or documents that need to be submitted? How long does it typically take for the application to be processed once the fee is paid? Is there a way to track the status of my application? Are there any potential issues or delays that I should be aware of?