When I try to type something it is shown with some prepared text
When i try to click the T button to create new text, it is shown already made some text example with a tag. This tag is hidden and if I click "show hidden character" it is shown with #.
Can I start with completely blind text function without this suggested pre-made alphabet arrangement looks like some word (but doesn't make sense, it is just look like preview of the text)?

The # symbol marks is included into any text at all, to help designers to see where text ends. There are other hidden characters that mark column breaks, paragraph returns, line breaks, special space symbols, etc.
The text that gets inserted when you create a new text helps to quickly see how text would behave on canvas with set font parameters. You can disable this option in Preferences > Type > Fill New Type Objects With Placeholder Text, if you find this irritating.