This article explains how to accept an invitation link to join a WhatsApp group on Android.
Steps
Step 1. Open the link you received via message, email or chat
Group administrators are allowed to copy and paste the invitation link anywhere for the purpose of adding new members.
Step 2. Click on the invitation link
WhatsApp will open automatically, bringing up a window on the screen.
Step 3. Search for the group name
You find it at the top of the window that has appeared. If administrators have set up a profile photo, the image will appear next to the group name, top left.
Step 4. Search for the creator's name
If you're not sure who invited you, you can see the creator's name under the group name. The word "Group created by" will appear at the top of the window.
Step 5. Review the member list
In the invitation window you can also see the list of all group members under the "Attendees" heading. You may find people you know there and get a better idea of the reason for the invitation.
Step 6. Tap the green button at the bottom right called Join Group
You will automatically become a member of the group. You will be able to immediately start sending messages, images and documents to the other participants.