Code to read and write IP/string to config file

I have a current diag program that has been written using windows forms, it has various tabs within the program to do certain functions. I would like to add a tab with two functioning buttons and one string input box. One will be a "Get IP address" that will get an IP address or string from a config file that is always in the same location and the string around the IP/URL is the same as well. The second button will be "Set/Write IP/URL address to Config" which will take whatever the IP address or URL string that is entered into the text box and place it in a few locations throughout the config file. Seems very simple from what I gather, just not experienced enough to tackle this. I have added the actual tab and some buttons with a text box in visual studio, but need the code behind it to make it work.