You didn’t say much about your computer. If it’s a Mac, then GarageBand would be all you need to get started. It has drums, built in amps, keyboard sounds, reverb, delay and will allow you to multitrack very easily. I don’t believe there is a direct PC equivalent but someone will chime in.
your first hardware acquisition should be an audio interface. A basic 2 input model from focusrite or Behringer under 100£ will get you going. It will plug into your USB port and you plug your guitar, mic, keys etc into it. You monitor through it using headphones or separate studio monitors. That’s all you need to get started. Good luck