Of course, playing cash table or MTT against real opponents is one of the best ways to start understanding poker as soon as possible. However, it's also important to note that this practice will only be effective if the beginner player has enough self-discipline to keep bankroll management and constantly analyze his losing hands after each tournament.
But playing cash or MTT are two very different ways. Someone who doesn't know the difference or tries to play the same way will be confused and will lose if they apply one strategy to the other. In general in an MTT it is best to try to hold, playing few hands at first, such as strong hands, pocket pairs and SCs, and then playing more and more aggressively as the blinds get higher. In cash, the blinds remain constant, so you don't have to vary your play in this way,