Since so many things block eruptions (the edge of the board, another cap, moving out of an empty space) it is almost always possible to move the caps around quite a bit to get them into place.
This usually involves moving caps towards the edge, which prevents eruption beyond it, and moving caps towards other caps, which prevent eruptions onto them.
Often the thinking and moving of caps is done simultaneously, as it can be difficult to plan out so many moves ahead. Some cap movements are legitimately reversible without causing an eruption, but most players will allow some "go-backs" as experimentation is done.
The more experienced the player, the more they should be expected to be able to plan this out in advance without needing to undo cap moves when an idea doesn't work.
1) So let's say you've determined that you want to get your cap to the big red X, so that you can cause an eruption (red arrow) that goes all the way to the end of that center row.
2) You move caps A and E diagonally as shown by the blue arrows. No eruptions happen, as eruptions can't go off the board. It doesn't really matter which order you do these moves in.
3) Now you move A into place to cause the eruption. No eruption happens because cap E blocks it. (Or you could move E upwards, with no eruption because A blocks it.)
You also want to get D out of the way so your eruption can go all the way to the end of the row, so you move it upwards. No eruption happens because it is blocked by C.
4) Finally, you move cap A to the right one square (blue arrow) causing the eruption to flow out to the far side of the board (red arrow).