Row 1 is the whole method. Block size is how far apart the subnets sit — count 0, block, 2×block… until you pass your address, and the one you just passed is your network.
Rows 2 and 3 are free: hosts is block − 2, and subnets is 256 ÷ block (per octet).
Everything below /24 is the same six numbers, one octet to the left.
Anything under 80% comes back more often in the drills. Get everything green and you're done.