Okay, join and meet are ways to connect with other people online. When you "join" something, it means that you become a part of a group or community. For example, when you join a soccer team, you become a part of that team.
When you "meet" someone online, it means that you connect with them through the internet. It's like meeting a new friend, but instead of seeing them in person, you talk to them through your computer, phone or tablet.
So, let's say you want to join a group of people who like to play video games. You might join an online community where people share information about their favorite games and play together. On the other hand, if you want to meet someone new from a different part of the world, you can use a video call app like Zoom or Skype to chat face-to-face over the internet.
In summary, joining is about becoming a part of a group or community while meeting is connecting with someone online.