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i think you are trying to connect the mc with pc right ?
for this first fetch the data by usart protocol (you can see this in pic data sheet ) then compare the codes that you fetched from system then according to that set the relay pin.
first thing learn some basic electronic stuff like switching using transistor,sensors etc
then learn basic c ( you need only basic c language in order to do embedded programing ) also try to learn assembly language this will increase your logic analyzing capacity.
try to read the projects in...