Select text in vertical in TeXstudio (or in any other Latex Editor) - Column Mode

In TeXstudio, you can select the blocks with ctrl+alt+shift+leftmouse+drag. But I find easier to do it with notepad++ (free) as advocated by @Sango.

I don't know of that feature in TeXstudio, i know it from UltraEdit. And there is the column mode in notepad++ (free), maybe that helps for a one-time use.

But if you want to fix the indentation, you can do that just by selecting the lines and then press Tab. There is also an indentation command in the idefix menu. If the indentation should be space instead of Tabs, this can be set in Options->configure->Editor "Use Spaces for tabs" (or something, i have the german setting enabled)

If you want to indent text in the line itself, that's another question. But that could be done via macros something like "Tab, move down, move left, tab...."