Oh. In that case, I don’t understand your question. What do you need help with, exactly? You asked in the Help section, which is for help with Aseprite specifically, so I thought you were asking about Aseprite’s tools.
If you’re asking about avoiding jaggies, then all you need to do is draw lines that are made out of equal-sized segments, e.g. slopes of 1/2, 1/3, 1/4, 1/5…
The Pixel Joint pixel art tutorial has a pretty decent explanation on avoiding jaggies in straight and curved lines (and is a worthwhile read in general): Pixel Joint Forum: The Pixel Art Tutorial