Have you ever played with magnets, especially tried to put two north poles together with your hands, and noticed how difficult this is? Well, although it is difficult, you can manage it. But this is only possible because the magnetic dipole force is weaker (proportional to $1/r^3$) than the coulomb force (proportional to $1/r^2$) that keeps your hands from falling apart.
When it comes to fusion, the situation is similar in that you would need to push positive nuclei intensely together in order to make them eventually fuse due to their shorter ranged strong interaction. But, sadly, there is simply nothing stronger at technological scales than the repulsive Coulomb force between the positive nuclei, because every machine we can build is made of atoms, which are also subject to the Coulomb force. Hence, no simple machine can push nuclei together to achieve fusion, unlike you are able to push magnets together with your hands.
The only way to achieve nuclear fusion is to increase the speed of the components in order to surmount the Coulomb barrier by their kinetic energy. But if kinetic energy is high, the probability that the nuclei just fly apart increases also, unless you are able to confine them in a limited volume. And this is the actual difficulty: you can't just put a plasma of several million Kelvin into a Cola bottle.
In the case of the fusion/fission bomb, the containment is simply achieved by the fission bomb creating an enormous pressure that acts on the fusion components. It is clear that this is a one-time event, and, as such, it is not a sustainable process like it is desired for a power plant. And you can't just slow down the fusion process, because this would again decrease the pressure, which wouldn't be sufficient then so as to confine the fusion components.