In bowling, 'scratch' means without the handicap added in. A scratch game is the actual score of the game, whereas a handicap game is the scratch game and the handicap added together. So 'high game scratch' would be the highest game a person in the league or tournament bowled without adding in the handicap. For example, someone with a 12 handicap bowls a 249. The 'scratch' score is 249, the handicap score is 261.
Video game is a software. A software is a program. So you need to know how to program. Programs are written with programming languages. Pick a language and master it. You might not need to build everything from scratch. There are tools that can make building game easier. But you still have to program.
I reccomend learning how to use "Scratch", that is a simple program you can use to make some games. After learning scratch, you could learn how to use "Yoyo Gamemaker", which is harder to learn, but if you are good with it, you could make a big profit. Google should be able to teach you how to use them :)