Tajen from: The WordPress MU Manual
Now that you have set up your MySQL database for bbPress and attached your username to the database you are ready to install bbPress following the steps outlined below:
1. Download the latest zip version of bbPress
2. Unzip the downloaded file to a folder on your hard drive.
Installing bbPress using FileZilla
You use FileZilla as follows to install WPMU:
3. Enter your domain name, your username and password. NOTE: the same username and password that you use to log into your cPanel.
4. Click Quickconnect
5. Double click on your folder to open up the root directory of your site.
6. Now you need to create a folder for your bbPress install by clicking on right clicking and selecting Create directory and create a folder called forum.
7. Locate and open up your bbPress folder on your hard drive.
8. Open up the forum folder on your site
9. Hold the SHIFT key, and press the DOWN arrow on the keyboard to highlight all the files and folders in the bbpress folder on your computer and drag it into your forum folder on your site.
10. Dragging the code from the bbPress folder on your computer into the forum directory of your site uploads the bbPress code to your site.
However it doesn’t complete your bbPress installation. Check this by viewing the location of your forum in a web browser. For example for edutags.net the forum would be located at edutags.net/forum.
You should now see instructions for installing bbPress.
To complete installation you need to:
a) Configure your database
b) Integrate your WordPress site
c) Change your site settings
Configuring your database
1. Click on “let’s get started”
2. In the Database configuration section you need to enter your database connection details.
These are the same details you set up in your cPanel i.e. you set up a database and username named wmpu and cPanel will have added your domain name to the front of each.
3. Copy the text on the next screen which you will use to create a configuration file.
4. Now open up a new Normal text in EditPlus and paste this text then save file as bb-config.php
5. Upload the bb-config.php by selecting the bb-config.php file on your computer and dragging it into your forum folder on your site.
6. Click on Check for configuration file
7. If the configuration file has been set up properly you should see the following screen and the next step is to click Go to Step 2.
Click Skip WordPress Integration for Step 2.
WordPress integration is designed to integrate the login and user data of bbPress seamlessly with your WPMU site so that you and your users can login to either your bbPress or your WordPress site and be automatically logged into both.
However set up WordPress integration with bbPress is extremely challenging even for those who have achieved it on previous installations.
TIP: You can always integrate WordPress later from within the admin area of bbPress.
8. You should now see the following screen and you need to click on Go to Step 3.
9. Add your site setting details and click Save site settings.
10. Click Complete the installation.
11. Final screen should show that your installation is completed. It displays your username, password and site address. You will also receive these details by email.