They are right. You can be taught the "code" but when it comes to comprehending it you are on your own. It is not something most, if not all, can just jump into overnight. Personally, it took me months to get used to programming in java. That being said, it was all still just basics and I had no idea on how to do anything complex. The only way to learn to program in private servers is to first understand the language. Then after you have that, you can look into the servers code, reading through it ALL, following the logic chain. Then if you have questions about how or why something works you can ask. There are quite a few elementary java tutorials on this forum.
Your first posts for releases on this forum will probably have a lot of criticism on them as well. (Typically basic programmers don't have the means of writing pretty or efficient code)
As you delve into the language as well you should start with the habit of DOCUMENTING your code. It is a bitch to change this habit once you started. (trust me)