I need to pin important links of SharePoint to the Left-Hand Rail in Microsoft Teams
Please check attached image for better understanding.
Click here to open the image.
The left rail is only for actual Teams apps, so you can't pin just a web link there directly. However, there are a few options:
Develop a custom "tab" app that you deploy into a local company store. See this tool (built into Teams from Microsoft) to try out creating an app like this: https://learn.microsoft.com/en-us/microsoftteams/platform/concepts/build-and-test/app-studio-overview
Use Viva Connections, which provides it's own rail (but you need an entire SharePoint intranet site for this
Use a third party app like Quicklinks which lets you add your own "bookmarks" app in the left rail, for multiple web links.