I want to use it for the incubator, how to add buttons to the desired temperature?
and when the temperature has reached the desired target, then it will activate the load (relay).
Incubator for what? What temperature range? What temperature sensor? You really haven't provided much information for a project having many ways to go about it. The LM35 Precision Centigrade Temperature Sensor is a popular choice for circuits like this as well as a host of others. You need to break your project down into sections starting with your choice of sensor, then range, then type of control. Going to drive a heater with this relay? How much current? The mention of buttons implies a set point that can be raised and lowered? Then I suggest you start getting friendly with micro-controllers. Do you have any programming skills?