Revisit moving text from title to text artist

i'm trying to understand the code and put the bits in their place. Can you check/edit as needed? I don't understand the last part so I put the ????

%artist% Take the contents of the field %ARTIST%
Busta Rhymes

$regexp use a regular expression with the following parameters

%title% take the contents of the field %TITLE%
Twerk It

(.*) capture any amount of any characters into the first capture group
Twerk It

( until you reach an opening bracket
Twerk It (

(.*) capture any amount of any characters into the second capture group
Feat. Vybz Kartel, Ne-Yo

) until you reach a closing bracket
Feat. Vybz Kartel, Ne-Yo)

$2 output the contents of the second capture group
Feat. Vybz Kartel, Ne-Yo

== unique separators for the next step - could be anything as long as it is unique

$1 Output the second capture group.
?????