"BO 1st at beginning of row then every following alt 6th and 8th row 24 times."
This is to bind off 1 st at the beginning of the next row. Then you will alternate the bind off on every 6th row and every 8th for a total of 24 times.
So, your work will look like this.
Next row (let say row 1): BO 1 sts a beginning of the row.
Row 2-6: Work even on these 5 rows so that the next row will be the 6th row bind off.
Row 7: A bind off row (this is your first 6th row the bind off). This counts as your 1 BO of the 24 times of bind off.
Row 8-14: These are none BO rows. Work even on these 7 rows so that the next row will be the 8th row BO. This counts as 2 of 24 times bind off.
Alternate every 6th row and 8th row bind off as above until you have a total of 24 times bind off. Your bind off rows always will be on the odd row or the right side.
Hope this helps and thanks for the question.
Have a great day!