First off, don't worry. You already have all the necessary tools you need.
Although the language you use to learn system & network programming doesn't matter much, it is better if you use C or C++ to practise and learn. This is because the kernel itself is written in C and exposes system calls that can be used directly from a C/C++ program. That said, "The Linux Programming Interface"(I am personally reading it) is a really good book. It talks a lot about how one should go about using system calls to get things done by the kernel. Make sure to read a little every day and try out the examples by writing C/C++ programs.
I recently realized that TLPI doesn't talk much about why are things the way they are(a very good example would be virtual memory and related stuff). You should refer some theoretical book for this. I suggest you go with "Operating systems" by Deitel & Choffnes.
Read man pages and practise using the libc/kernel APIs. For example, if you want to know about flushing, read 'man 3 fflush'. This might be needed when you want to flush all the input/output data that has been buffered by the C library before you can get fresh input from stdin. For example, if prompts are buffered, you definitely don't want to "scanf" before you have flushed the buffers. If you want to learn network programming, read chapters related to socket and refer 'man 2 socket'.
You will eventually get to a point where you will be able to connect all the dots(APIs) and be able to figure out what exactly you will need to get some problem solved.
Finally, don't learn for a future job. Learn for yourself. This will help you in the long run.
Day-to-day tasks that, today, involve usage of plastic were possible even before its discovery and wide-spread use. Maybe, yes, plastics have made many things easier, but, if we can all come to the conclusion that plastics are more bad than good, then we can all get rid of it.
It is also likely that an alternative to plastic will come up one day(maybe it already exists). It is also likely that people figure out a way to effectively reuse used plastic(maybe it already exists). But, what about the harm that has already been done? For that, not only do we have to go out and collect thrown away plastic scrap but also figure out what to do with it. We also want people to properly segregate plastic wastes at their sources as well.