I used Paint to do pixel by pixel line diagrams, such as wiring circuits and simple mechanical diagrams. When I moved to Linux it took a while to find a suitable alternative. There are several graphics programs but most seemed to be too sophisticated. I now use a program called Pinta which does all that Paint used to do for me. There is a Windows version of Pinta if you want to check it out. Like most Linux software it is free to use, donations are accepted.