Gustavo Bravetti ·
Check this link if you want to understand about digital filter design, it start from very basic filters and then go a bit deep, also you can get a .pdf version of the whole tutorial.
http://www.dsptutor.freeuk.com/dfilt1.htm
If you have any questions about the content of the document you can post it here.
Good luck DSP enthusiasts! 🙂
C ya