The main software is Stable Diffusion. There are mainly 2 user interfaces that is the most established. Automatic 1111 and ComfyUi but there are also others such as Fooocus (a simplifyed UI).
Regardless which user interface you choose, the software is still Stable Diffusion.
There are different model generations, just like there are windows 7, 10 and 11 etc. The ones that are used the most are SD1.5 and SDXL. I would recommend either going with Automatic1111 or Fooocus to get started, when you have become proficient with it, then try a less beginner friendly user interface such as ComfyUi (node based UI) if you wish.
How to install Stable Diffusion Automatic1111:
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How to get started Using SD A1111:
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Stable Diffusion Fooocus tutorial:
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*Edit
Something to be aware of.
Fooocus is primarily using SDXL.
It is supposedly lighter on the vram requirement compared to A1111 though.
I don't know if you can download SD1.5 models and use with it.