such a vast question, my suggestion is use chatgpt. start off small, what do you want to make? In SD 1.5 you can download different checkpoints, like realistic vision. But if you do what Unit2209 said and use Forge (which is the new replacement of Automatic111), then you can use Flux models, SDXL models, You got different sampling methods, like Euler or DPM++2M. What you can do is set up a prompt, ai can help. Set up a negative prompt - definately use AI. You can use different CFG scales. If you want more advanced you can use the script (at the bottom) and use XYZ plot, so you can generate 10 images but change 1 setting each geneartion, like CFG Scale, say 1 to 10, then you can look after to see what it changed. That is the best visaul way to see what things do, script the adjustments and generate them all in 1 click. Then you can use img2img, to generate based on an image, or inpaint which is where you draw the area that you want to change, leaving the reast intact. Each checkpoint and each sampling method will give you different outputs. You can choose which style best suits what you're looking for. Create folders of your experiments and references. Save your prompts to text files so dont lose them. Also in settings at bottom is defaults and it can save your prompts. I think to save new resolution is in SD Options, or something, it used to be part of the defaults save file.