Andrea, in Cut&Paste mode, "c" copies a highlighted area into Cinelerra's cut buffer and you will not see anything change on the screen. The "v" pastes what is in Cinelerra's cut buffer ONTO A BLANK SPACE on the timeline -- you have to create a blank space of any size to put the cut buffer.  Highlighting an area or inserting a blank space(s) allows the v to insert the cut buffer.