OK, please help me and tell me what's confusing. I'll adjust the texts then.
Allowing WASD plus cursor, I guess this is to support both left and righthanded players. But introducing these in the order that you do is too much information. I would just introduce ASD first, then W, then either allow the keys to be programmable or add a note that alternatively you can use the cursor keys. Also there's nothing intuitive about W / up for rotate, but it seems you're forced into this because you want the basic tetris controls to be done with a single hand so that the other hand can use the mouse (dunno how to improve this).
"Drop the piece inside the red rectangle" -- I should be able to clear this message with a mouse click, and then press the drop button. Also, by default it should be lined up to drop inside the rectangle.
"I recommend .... at your left" -- this comment is unnecessary at this early stage.
"The construction doesn't respect the plan" is a bit annoying because in the absence of hammer / knife, the initial sequence of shapes might make this unlikely. I feel as though I am doing something wrong when I am just learning the controls. Make the initial shapes so simple (maybe just square blocks of 4) that the construction will respect the plan unless I drop outside the shape. It's too much to ask the user to plan ahead at this stage -- this is just a tutorial.
The drop button should be disabled while a dialog is up and the dialogs should always be absent when you're actually supposed to do something. This was a big source of confusion. Or you could just move the instructions away from the play area, e.g. to the left.
At the end of the first part of the tutorial the default "skip" action (left click) restarts the tutorial, whereas most users are likely to want to move on at this stage. Have the default action move on and escape restart.
Second tutorial level: using the hammer costs 2 secs in time mode but time mode is disabled. This is too complicated, you're just trying to introduce the hammer. Forget about the costs / time limits (including the "-2 secs" fading text) and don't mention them until a later level; introduce them at the start of that level.
Also, a minor bug: I get some flickering widgets, including the tutorial dialogs, and the blue bars at the side of the play area. This may be related to the fact that I alt-tabbed out of the game, then back in?
Fine to support single mouse button users but for those of us blessed with 2 buttons, right click to drop would be nice!
Also, tool pointer should change to something else while over the drop button, otherwise it seems as though I want to smash it (!)
For the knife, the state machine is a bit weird, it unnecessarily requires two presses. Selection of the cut square should be finalised at the point when the mouse button is first pressed, a ghosted square should appear while you drag it, and then it should be placed with the button being released again. Also the knife icon should change during the drag period (and perhaps change again if the current destination square is disallowed).
I guess you could consider changing the knife to a robotic grabber or something, just an alternative metaphor I guess.