I have imported two text layers into QGIS but now I am not able to edit them. All the editing fields are grey. I don’t use QGIS that much, so it’s a stupid question.. But how can I activate the edit functions?
Last I checked, QGIS can't be used to modify CSV, XLS, or ODS spreadsheets. If you import the spreadsheets and convert/export them to points or line-based shapefiles, only then will you be able to modify their contents by hand.
Your best bet for doing simple modifications to raw text files is to open them with nano/vi/vim, notepad, gedit, or another similar text/code editor.