I'll second the recommendation for http://nuclearweaponarchive.org/ , especially the "nuclear weapons faq" section, it's a great site though some of the material can be heavy going.
Thermonuclear bombs use a multi-stage design. A nuclear bomb (such as a fission bomb) can be thought of a bit like a light-bulb, only an extremely bright one that is so hot it shines mainly in the x-ray spectrum. A multi-stage thermonuclear bomb takes the light from a fission bomb and traps it inside of a "hohlraum" which is a fancy german word for a box or chamber that happens to be made out of very heavy metals (often depleted Uranium) that is reasonably opaque to the soft x-rays emitted by the nuclear explosion.
Of course, no mere metal container is going to contain the energy of a nuclear explosion for long, the inside surface layers of the hohlraum will absorb some fraction of the x-rays and be vaporized (this is called ablation). This ablation of surface material is so energetic it creates a thrust, like a rocket exhaust coming off the surface of the material it pushes the material away, blowing up the hohlraum like a balloon. The same forces play out on the other occupant of the hohlraum, a capsule containing fusion fuel (often lithium deuteride paste) with a shell made out of similar "high-z" x-ray opaque material. The ablation of the surface of the fusion fuel capsule creates incredible forces, powered as it is by the energy of a nuclear explosion. This causes the fusion fuel capsule to implode, creating conditions of extraordinarily high matter density, pressure, and temperature (due to adiabatic heating). At the center of the fusion fuel capsule there is a fission bomb core, a chunk of Plutonium or Uranium. Because of the speed and strength of the "radiation implosion" (though strictly speaking it's a radiation powered ablation implosion) the amount of fissile material can be small compared to a chemically powered implosion design (keeping in mind that critical mass goes down as density goes up). This "spark plug" then kicks off a super critical fission chain reaction which starts releasing energy that heats up the fusion fuel and kicks off a fusion chain reaction. The fusion reaction then releases a metric crap-ton of very high energy neutrons which facilitate fission reactions including fissioning of depleted Uranium (U-238) in the bomb components (such as the hohlraum, the tamper around the fission primary, the fusion fuel capsule casing, etc.)
In principle, much is the same. The main difference is that the explosive force to implode the main bomb (or the "secondary") comes from a nuclear explosion.
Thermonuclear bombs use a multi-stage design. A nuclear bomb (such as a fission bomb) can be thought of a bit like a light-bulb, only an extremely bright one that is so hot it shines mainly in the x-ray spectrum. A multi-stage thermonuclear bomb takes the light from a fission bomb and traps it inside of a "hohlraum" which is a fancy german word for a box or chamber that happens to be made out of very heavy metals (often depleted Uranium) that is reasonably opaque to the soft x-rays emitted by the nuclear explosion.
Of course, no mere metal container is going to contain the energy of a nuclear explosion for long, the inside surface layers of the hohlraum will absorb some fraction of the x-rays and be vaporized (this is called ablation). This ablation of surface material is so energetic it creates a thrust, like a rocket exhaust coming off the surface of the material it pushes the material away, blowing up the hohlraum like a balloon. The same forces play out on the other occupant of the hohlraum, a capsule containing fusion fuel (often lithium deuteride paste) with a shell made out of similar "high-z" x-ray opaque material. The ablation of the surface of the fusion fuel capsule creates incredible forces, powered as it is by the energy of a nuclear explosion. This causes the fusion fuel capsule to implode, creating conditions of extraordinarily high matter density, pressure, and temperature (due to adiabatic heating). At the center of the fusion fuel capsule there is a fission bomb core, a chunk of Plutonium or Uranium. Because of the speed and strength of the "radiation implosion" (though strictly speaking it's a radiation powered ablation implosion) the amount of fissile material can be small compared to a chemically powered implosion design (keeping in mind that critical mass goes down as density goes up). This "spark plug" then kicks off a super critical fission chain reaction which starts releasing energy that heats up the fusion fuel and kicks off a fusion chain reaction. The fusion reaction then releases a metric crap-ton of very high energy neutrons which facilitate fission reactions including fissioning of depleted Uranium (U-238) in the bomb components (such as the hohlraum, the tamper around the fission primary, the fusion fuel capsule casing, etc.)
In principle, much is the same. The main difference is that the explosive force to implode the main bomb (or the "secondary") comes from a nuclear explosion.