To install Microsoft Office from portal.office.com, sign in using your Microsoft account credentials. Once logged in, click on "Install Office" from the home page. Select "Office 365 apps" to download the installer. After the download completes, open the installer file and follow the on-screen instructions. The installation will begin, and once finished, launch any Office app like Word or Excel. Sign in with your Microsoft account to activate the product. Ensure your device meets system requirements and has a stable internet connection for a smooth installation process. Enjoy access to Office applications for productivity and collaboration.