To send an application to join the group, do the following:
Go to the "Tasks" section
Create a new task
In the subject of the task, write "Application for joining the group", in the description - a short explanation of why you want to get into this group
Assign a task to the group you want to join
Submit the task
The group administrator will receive your application and will be able to add you to the group, or write down why this cannot be done.