To add a new section in STAAD.Pro CONNECT Edition, please refer to the wiki below
(40) How to add a new section in STAAD.Pro ? - RAM | STAAD Wiki - RAM | STAAD - Bentley Communities
To add a new section in older versions of STAAD.Pro (V8i), please download the video file
Please ensure that you are logged in. Once you are logged in, you will be able to see the blue Download button on the right.
The Download button would allow you to download a zip file named Adding Section to the SectionDB.zip. Unzip the file to get a movie file named modifying the SectionDB.wmv which is a video explaining how to add new sections to an existing section database in STAAD.Pro v8i.