Pressurized steam is used to heat the material to be sterilized. It kills all microbes, spores and viruses. Autoclaving kills microbes by hydrolysis. The intense heat comes from the steam.
2. Flaming and baking
Microbes are killed by by oxidation of cellular components. It needs higher temperatures than autoclaving.
Filters work by passing the solution through a filter with a pore diameter that is too small for microbes to pass through. Viruses and phage can pass through filters.
Ethanol or isopropanol denature proteins through a process that requires water. They are good at killing microbial cells but they have no effect on spores.
UV, x-rays and gamma rays are all types of electromagnetic radiation. They can penetrate DNA.