You can safely create commercial applications - bar the compiler itself - since there is a linker exception.
You can also create commercial applications - bar the gui itself - with the Lazarus standard components for the same reason.
There is a caveat, though: if you use e.g. OPM to install other components than the standard ones, you will need to check the licenses.
They are all open source licenses, but not every open source license is compatible with closed source applications, e.g. GPL without linker exception or BSD licenses.
What is always OK is GPL with linker exception and MIT licenses. There may be more, like the SQLITE license, which is extremely liberal, or open source without any license attached.(it usually says "use as you like"
Note: you should always adhere to copyright, it may be that an author demands you mention its use in an aboutbox or documentation. That is because of misrepresentation as your own code is not allowed in such cases.
Copyright differs from license, though.
To summarize:
1) check the licenses
2) check the copyrights
important if you sell large volumes:
3) check software patents, this is a difficult one, because most algorithmic ones are thrown out in the EU for example, but valid in the USA.
4) the latter means that you need a good functional design documentation (IMHO you need that anyway for commercial software, but in the above case you also need it for legal reasons)
5) If these patents are thrown out in e.g. Europe because of prior use, the USA is also safe. You can claim prior use in the USA too, based on the EU's (any country in the EU too) judgement. This happens all the time.
And (1,2) you are legally OK in most cases except in countries (3,4) that recognize software patents. (Note 5)