An immigrant is someone who moves or comes to live in a new country, usually with their family. And sometimes, as people grow old or have families of their own, these groups of people are divided into generations.
The first-generation immigrants are people who were born in another country and moved to a new one. They might speak their native language better than the language of the new country. They might also have differences in culture, food, clothing, and habits.
Then there are second-generation immigrants, who were born in the new country but have parents who were born in another country. They have grown up in a mix of new and old culture, and they may speak both languages.
Third-generation immigrants are people who were born in the new country, and their parents and grandparents were also born there. But their family heritage may still have many traditions from their original homeland.
In short, generations are a way of understanding the differences in culture and identity between people who come from different places but now live together somewhere else. It's like being part of a big global family!