Ok, you decided to create a tag cloud at your ucoz web-site, What to start with? First, go to the upper menu. Click Builder---Enable builder.
Now click Add Block+ in the same submenu. Drag the new block to any place in the main menu.
Name the new block "Tags Cloud". Now click on the gear icon in the new block. You'll see such a menu:
Here choose Widgets section, therein scroll down and choose 3D Tag Cloud. Click Apply then. Voila!
After making all this don't forget to click Save changes in the Builder menu.