I'm building a DIY pedal effect for my electric guitar and I have to connect the input and output jack connector, but I don't know how to do it. The connectors have 3 pins, one is the tip which it is connected to the tip of the male jack and one I guess it is the ground, but I don't know how to connect the third one. My question is: can I use two mono jack input? In internet I saw stompbox with only one mono jack as output and one stereo jack as input. If yes, how do I have to connect them?
Have you studied the relevant wikipedia page ?
All the way down at the bottom right is a picture which shows you how to connect 6.3 mm stereo and mono jacks.
Many battery-powered effects pedals use the input conector as a power switch, connecting the negative side of the battery to the ring terminal of the jack, and depending on the mono plug to connect the ring terminal to the sleeve (ground) when the plug is inserted.