A computer games tester works for a computer games development firm, playing games and spotting bugs and offering suggestions for better gaming experience. They play the games systematically and in different ways for several dozens or hundreds of times, looking for errors, omissions or difficulties in gaming experience. They provide suggestions and guidelines to developers and designers, so that they can make sure finished version reaches the market.

Usually there will be a team of computer games testers or quality assurance testers, who will test the performance of the games at different levels and versions. You will also analyse the performance of the game, its interface, entertainment value, etc. You will also check for graphics, spellings, etc. Your duties also include making sure the game doesn't violate copyright rules.