The sequence goes like this:
- the missile is ejected from the silo by mortar system, that generates a huge amount of gasses under the missile to push it out, acting on a piston part located right under the missile
- the missile jumps out of the silo and the piston is ejected sideways via a small solid rocket motor
- some wiring harnesses and what looks like guide wheels is ejected from the missile
- the first stage engines of the missile (in this case liquid & hypergolic) are ignited and the missile starts to climb
This technique keeps the silo pretty much intact, which is nice for an ICBM acting as a space launch vehicle. Also IIRC for war use, it was theoretically possible to reload the silo and fire another missile before a retaliatory strike could destroy it, causing all kinds of havoc in cold war scenario planning.