Each of the grayed out options relates to a feature that is not utilized or capable of being used at the moment in a similar way as that reset position one. For instance, if you create a scatter plot and the data would not support a Forecast, then the forecast option will be greyed out. Hidden data is data that has been hidden as explained here - Show or Hide Missing Values or Empty Rows and Columns
I suggest reviewing each of the menu items in the online help as you become more familiar with Tableau to better understand why some of the features are not available. Sometimes it could be related to the data source, the values in the data itself, or the view currently selected with the data and field types selected. The disabling of features is meant to prevent confusion about what is currently available to be done with the view though.
I hope this helps.