HI Catkin. To progress with the next phase, really the whole instructions (the extra letters) are required. The instruction words have lengths 5,3,7,2,5,4,3,5,3,4. The first 6 words are an instruction as to what to black out and the last 3 words are an instruction as to what to erase.
Read the first instruction very literally. If it says "Black out letters in alpha beta" then every occurrence of the letters a,l,p,h,b,e,t should be blacked out.
Applying this instruction, and the second instruction, results in a grid which, when interpreted row by row, gives a coded representation of the message.