Roberto, you really should watch some of the introductory videos that Tableau provides. It would help you understand what you are seeing much more clearly.
To answer a few of your questions:
1) Tableau is not a data entry tool. Your stakeholder cannot update anything in Teradata from Tableau. (See below for a note on this.)
2) The "abc" that you see is Tableau's placeholder for a measure value. If you do not have any measures you wish to display, then nothing will show up here. You cannot remove it but you can hide it in certain circumstances.
3) By default, Tableau allows 6 columns of data to be displayed before it concatenates columns in the view. You can modify this by clicking on the "Analysis" menu item, selecting "Table Layout" and then "Advanced..." In the dialog box that appears, change all the "6" values to "16" (the maximum value).
4) Exporting the table will probably work but you may see unexpected results - hard to predict because it's highly dependent on what you are doing with the visualization you create. In particular, if you try to export 500 rows of data, you may get odd pagination results depending on how you do it.
A note on "updates" in Tableau. I suspect what you actually mean by "update" is "load and display the new rows that get added to the table every day". Tableau will do that with no issues. However, if you mean "add new or changed values back into the source database", this is not possible without using an Extension. That is a fairly new, and fairly advanced function. If that is what you mean, search the Tableau online Help for "Extensions".
Lastly, while you can do what you are doing with Tableau, this is far from its intended purpose. You may find that certain things you wish to do are more complex than you think they should be; that is because Tableau is a visual analysis tool, not a rows-and-columns reporting tool, or a data export tool. It can do those things, but not in a particularly friendly or satisfying way.
2) How can that column bi hidden?
Re "updates" Yes, I meant that for example, if you are my stakeholder, you can go an change the range you wanna see the data from. So you select from X date to Y date and only date from that range will show.
You can't hide it on a worksheet; if you place the worksheet in a dashboard, you can size the worksheet within a dashboard container so that you cannot see that column.
The date filter as you have described it should work fine.