How can I effectively repair termite damage and replace the deteriorated clapboards on my old detached garage while practicing my carpentry skills?

Our garage is pretty old, it was added sometime after the house was built in 1890. We’ve had it for two years now and I’m finally getting around to cleaning it out and starting some projects. I could really use some advice on how to tackle these repairs. It’s just wood clapboard and there are some spots with termite damage. I haven’t done much carpentry work before, but I think this could be a good place to start practicing. Any videos or tips would be much appreciated.

In the first picture, there’s a stud that had termite damage and the previous owner covered it with rubber for support. Unfortunately, that stud is pretty much disintegrated. The second picture shows the lower clapboards that need to be replaced. And in the third picture, you can see the piece of wood at the bottom (sill) that needs about 20 inches replaced due to termite damage. I’m not sure where to begin with that one, to be honest. Any help would be great.

Lastly, pictures four and five show the bottom of the garage door. Termite abatement was done before we bought the property, so this damage is from a long time ago.