Hi. I use Inkscape on Yosemite 10.10.2 and I have following problem. When I started to use the software, everything was OK. But after doing several operations I've observed that calligraphy tool doesn't work properly: When I try to use it, there is no visible effect except disappearing red traces. Also some other tools have no visible effects. Could anyone help me?

Hi.

Most likely your stroke and fill colors is set to the same color as the background.
Bring up the "Stroke and Fill" dialog box by typing Shift Ctrl F
Set your fill and stroke to something visible.

To see if it's "something" on your "page" - (called canvas in "Inkscape lingo") -
enable outline mode by typing Ctrl - 5 or go to View - Display Mode - Outline
(Use the "5" key on the numerical keypad.)

For some help take a look at When A Tool Stops Working at the Inkscape Community webpage.

Have a look at The Manual.
I recommend going through the tutorials in "Quick Start" section.
This will get you up to speed in no time!

Great! It works properly. Thanks!