You haven't installed Allegro or you have installed it incorrectly. Read section
Insallation and use in file ~/README.md and follow the instructions.
I've compiled the examples without errors but they don't work and they don't show any error message. What's wrong?
See question Why al_init returns False? below.
Go to the ~/src/examples/ directory and open them. The ones with numbers
introduce different concepts in order. The other show some advanced concepts.
Also, there's a tutorial in the web site named Vivace . It shows how to use Allegro.pas in an actual game.
Finally, there is a complete game in the src/demos/ directory, with comments
explaining how it works.
The main reason al_init fails is because the library version is old or it is
not compatible.
Look at the beginning of unit allegro5. There are some constants that define
the version number. Compare with the version of your liballeg installation
and update if needed. If your liballeg is newer, maybe you need to downgrade
it. Allegro.pas should work with Allegro 5.2.6 and up.
Remember that only the two first numbers of the version are the same in both Allegro and Allegro.pas.