To join Communities, you need to have a Bentley User Profile -- it is free and takes very little time to set up.
Create a Bentley User Profile
First, click the "sign-in avatar" towards the upper right corner of any Communities' page.
Click the "Register" link.
A simple form will then be presented -- fill-in the information requested and then click "Submit". Then, follow the instructions to verify and complete the Bentley User Profile creation.
Once that is done, you should be able to sign in to Bentley Communities.
You only have to do the above one time. From then on, simply click on the "sign-in avatar" and enter your username and password that you entered for your Bentley User Profile and you can then use Bentley Communities.
After you have successfully signed in, you can navigate to one of various working areas and begin engaging with other Communities members. You can go to Product Support page for an easy way to do this.
Troubleshooting: If you encounter strange behavior or an error during or after signing in, we suggest signing out of all *.bentley.com web browser sessions, close all browsers, and then sign back in to Communities. If that does not work (or you continue to see strange behavior) you might want to try flushing browser cache and delete *communities* cookies.
If you continue to encounter issues, please let us know through the contact us form. Include any messages or errors you are getting.