I have an excel sheet, I want to sync it with SharePoint Foundation 2010 list and vice versa.
Two-way data connection is not possible with Excel. You can add data to the List and refreshing connection in Excel will bring the data from the SharePoint List, but you can't add data in Excel and sync to SharePoint List. More information about Excel Sync is here.
However, this is possible through MS Access. More information about Access sync is here
To complete the previous answer, it is actually possible to do two-way data synchronization between Excel and a SharePoint list, but you need to use third party products, such as the one my company has developed: SharePoint list Synchronizer.