Lazarus is open source, you're free to use it in any project you like including commercial projects.
But if want to support Lazarus/FPC, there are many things you can do:
- Donate to Lazarus
https://wiki.lazarus.freepascal.org/How_to_donate_to_Lazarus- If you have project but limited time or manpower for it, you can consider to create bounties
https://wiki.lazarus.freepascal.org/Bounties- If you have time and have decent skill in programming, you can join in the development team, fixing bugs and make Lazarus and FPC better.
- If you good in writing, please help us improve the wiki and documentation.
- If you found something not working as what it should be in Lazarus or FPC software, please report it to the bugtracker
https://bugs.freepascal.org/view_all_bug_page.php?project_id=1- If you can spare some time, please consider to visit the forum and help others.
Although Lazarus and FPC are free, if you want develop and distribute commercial software using Lazarus/FPC, you should make sure you comply to the licenses' terms of components you used especially if you use any third party components.
You should already read this:
https://wiki.lazarus.freepascal.org/Lazarus_Faq#Licensing