Step-by-step: How to Create mosaic:
1 - Menu - File - Open Library...(If the Library is already open - you may omit this step). 3 - Set X and Y tiles number you want. You'll see area that would be converted to mosaic. You may 
modify/resize this area using mouse or using arrow keyboard keys. To expand mosaic area to maximum 
press Max button.
4 - Press Apply button and save a project file (*.mzp).
6 - When image will be mosaiced select from Menu - File - Save - project. This will save rendered 
Mazaika project. 
Below is a bit more detailed description of the same process.
First of all - open an existing tile library or create a new one.
Next, select a target image and divide it into cells.
Hit the  button or select Open source image  from the File menu.
 button or select Open source image  from the File menu.
When you see your source image in the Source image setup 
window, select the number of columns 
and rows that you want.
You may move and resize selected area of the source image with mouse or keyboard.
When the area of the image that you want to mosaic will be selected, press  Apply  button. Program will 
ask you to save Mazaika project file (*.mzp). After the project is saved you will see your source image in 
the main program screen.
To start rendering select
Mosaic - Mosaic All,
Mosaic - Random mosaic or 
Mosaic - Smart mosaic  
from the Mosaic menu.
Or you may press Render mosaic button -
Render mosaic button will start rendering in a default render mode.
You may change default render mode in the Preferences screen.
To render only a part of source image you may select cells on the main screen or use Mosaic Mask 
Tool 
If more then one cell is selected and Inv select checkbox is not checked then only selected cells would 
be rendered.
If Inv select checkbox is checked then only not selected cells would be rendered.