First, you need to get a DAW, and usually, with most DAWs you will get stock plugins to begin with. There are also a ton of free and paid third-party plugins to try out depending on the music you make.
Below are some of the free DAWs:
- Cakewalk by BandLab
- PreSonus Studio One Prime
- Stagelight by Open Labs
If you can spend some money then you should consider getting FL Studio or Ableton Live to begin with and both of them will give you enough plugins and tools to work with.
If you are an absolute beginner, you're in luck as there are literally thousands od resources to learn online for free.