Raglan Jersey called Paintbox Cardigan

For back of Jersey shape raglan. Instruction says Dec 1 st at each end of next and 8 foll. 4th rows then on fill 12 alt. Rows.

Not sure what it means can you please explain.

Welcome to KnittingHelp!

Decrease at each end of the next row (row 1) and then every 4th row until you’ve decreased on 8 following rows. So you would dec on rows 1,5,9,13,17,21,25, 29 and 32.
The 12 following alternate rows would be every other row 12 times: rows 34,36,38,40 etc.

Thank you so much for your help. Most appreciated.

Nice looking sweater!