Voip Software design

hi, im interested in learning how to build a VOIP app to use among my
friends and peers, maybe do video conferencing as well.I need some
information how on this works.
im a programmer with the very basic knowledge in promgramming and
database design.
Please someone direct me to where i can get this information and also a
p2p voip.
thank you very much
katsz

kattszd@gmail.com