I don't have a deep knowledge of Delphi and Pascal...
You don't need a "deep" knowledge, but you'll need at least "some" knowledge. Contributing to Lazarus is nothing for beginners. But every average programmer can contribute, no need to be a super-crack.
Focus on some topics which are interesting to you. Try to understand the examples provided with Lazarus or in the wiki or somewhere in the Internet. Read the users' questions in the forum. Try to understand them - many questions do not provide enough information, learn to see what is missing, run the demo programs which are sometimes added to demonstrate the error. Try to answer the questions, at first for yourself, then post your answer. If necessary write a little program to verify your answer.
Sometimes, out ouf a sudden, you'll understand things which you did not understand before. Since usually many people have the same difficulties like yourself write a tutorial or documentation in the wiki on your experience how you solved that issue. Everybody can contribute to the wiki! You don't need any permissions.
Write small improvements for the routines and components that you use but which bother you somehow. You may post that code here in the forum, and hopefully somebody else will take care of it. But it's better to learn svn and to learn how to write a patch. Look at the issues posted in the bugtracker and try to understand what developers need to process a patch.
Finally post your own patches to the bugtracker. I promise, it's a great feeling to see your first patch in the next release!