Question1,2

1.Why I am able to be in the community before in your circles?

Communities are an incredible feature from Google Plus. Since their launch, there are around 50,000 listed communities on Google+, some with tens of thousands of members, others with much fewer.
No matter whether you are into photography, business, education, fashion, or just about anything…there could well be communities already available for you to join, or you can make them yourself…It is a little like forming or joining a tribe!

Google Circles are a way to group people together based around the relation you have with people. You may have circles for different members of your family, work colleagues, interest groups etc.
Below is the system I use to tame the flow in my Stream…
 

2. I want to hangout with your community instead of individuals, how can I do?

Android app

1. Open the Google+ app .
2. Near the upper right corner, touch the down arrow .
3. Touch My Communities  > Find more communities > in the upper right corner, touch the search icon .
4. Type what you’d like to search for > in the lower right corner, touch the search icon .
5. To open the community's page, touch the name of the community.
6. If you find a community you'd like to join, touch Join community.

Computer

1. Open Google+.
2. In the upper left corner, click the drop-down menu   > Communities .
3. In the upper right corner, find the search box with the text: “Search for communities.”
4. Click the search box > type what you’d like to search for > Enter.
5. To open the community's page, click on the name of the community.
6. If you find a community you'd like to join, click Join community.

Mobile browser

1. Open Google+.
2. In the top left corner, touch the navigation menu , then Search.
3. Near the top of the screen, touch the search box.
4. In the search field, type what you’d like to search for.
5. Touch the text next to "Show results for" and select Communities.
6. Results will appear below. Touch one to visit that community.

iPhone/ iPad app

1. Open the Google+ app .
2. In the top left corner, touch the menu icon  > Communities .
3. In the top right corner, touch the search icon .
4. Type what you’d like to search for > in the lower right corner, touch Search.