Microsoft Teams is a tool for communication and collaboration that is included in Office 365.
Fig. 1 shows the Microsoft Teams interface (with my organization's Teams, channel's and conversations covered up).
Fig. 2 shows the list of tabs at the top of a channel.
Click the [+] button to add display the "Add a tab" dialog, as shown in Fig. 3.
The "Add a Tab" dialog lists templates available on which to base your new tab. Click the "Website" button (Fig. 4) in this dialog. To find this button more easily, you can filter this list by typing "Website" in the "Search" textbox.
The "Website" dialog displays, as shown in Fig. 5.
At the "Tab name" field, enter a name to display in the tab list, identifying this tab.
At the URL field, enter a URL accessible by team members. This can be external or internal; but it must be an SSL site, so it must begin with "https://".
If you check the "Post to the channel about this tab", a message will be added to the "Conversations" tab with a link to the new tab.
Fig. 6 shows a new tab with the https://microsoft.com site displayed.
Fig. 7 shows the link in the "Conversations" tab. Users can click the link to navigate to the new tab.
You have now learned to add a new tab pointing to web site. The real power of this is if you create and deploy a custom site that adds functionality useful to your team members and publishing that site on the Internet or your corporate Intranet, where users can access it through Teams.
If your organization uses Office 365, it is likely that you have access to Microsoft teams. If you do not, call your organization's IT department and ask them: "What's the problem?"