Chacha20 - Explanation

[stamun8]

Is there any explanation about the format of Chacha20. The example is

Code:

15400 ChaCha20 20 $chacha20$*0400000000000003*16*0200000000000001*5152535455565758*6b05fe554b0bc3b3

$chacha20$*???????????????????*??*????????????????????*plaintext.................*ciphertext
Where nonce should be and is there anyway to bruteforce both key and nonce, if you know plaintext and ciphertext from ChaCha20 encryption?

Thanks