New knitter needs help please

I am new to the knitting hobbie and am trying to teach myself I cant seem to figure out how to cast on a stitch after placing stitches on holder and before finishing the rest of a row can someone please help me

Use a knit or cable cast on. Move the needle with the rorking yarn to your left hand, cast on the st and move it back to the right and work the rest of the row.

thank you so much ive tried for hours trying to figure that out its not explained in any of my how to books. I’m also new to this site so i really do appreciate the help again thanks and happy knitting to you