To share a File or a Folder from Teams, it is easier to do so from SharePoint.
Within Teams, if you navigate to the Folder structure first, then select Open in SharePoint
Then in SharePoint, if you want to share a Folder...
Select the Folder in question (remember, everything within will also be shared), then click on the Share icon
The default option is to Specify a person, group, or email. However, by clicking on the highlighted you can choose to share with everyone in MB (when you share the link) and you can choose whether editing is allowed by other people.
Once you've made your selection, click on Apply which returns you to the 'Send Link' pop-up. You can then choose to enter an email address of individual or a Group and click Send, which will email the link to the recipients... or, you can click on Copy Link and the SharePoint URL will copy to your clipboard so you can use this in your own communications.
To share an individual file... the process is very much the same.
Select the file in question, then click on the Share icon. Then follow the steps just as above, remembering to add 'Allow editing' if you want the recipient to be able to edit.
For more on how to use Teams and SharePoint, please refer to the training link videos from the Knowledgebase page.