Definitely. Yu-Gi-Oh began as a manga series and its success led to the creation of other related media such as the anime and the card game. The manga laid the foundation for the entire franchise.
Sure. For example, there might be variations based on different creative teams or targeted at different audiences, resulting in two separate Yu Gi Oh manga.
You can start by getting familiar with the characters and the basic plot. Then, pay attention to the details in the panels and the dialogues. That usually helps.