The hotbar in Factory Town is located down in the middle of your screen, making it easier to quickly select frequently used tools and buildings. It is not directly obvious that the items in the hotbar can be customized.

In order to use the hotbar more efficiently, it makes sense to change it to your own preferences. To do this, select the desired item in the build menu (opens with "B"). Then the item is placed in the hotbar using the key combination Shift + Number (a number in the hotbar from 1-8).

The black bar down in the middle is called hotbar.

There are several hotbar tabs, which you can switch between with F1 - F4. So it is possible to include a total of 32 items in the hotbar. My setup of the four bars looks like this:

F1: Items that you can always use well.
F2: Frequently used factories and the well.
F3: Slides, conveyor belts and structures for bridges.
F4: Pipes, rails and workers.