The answer to your selected question is shown below.
The simplest answer to this is that they don’t lock, well not in the usual definition of locking, apart from maybe the manual operated doors, which have a locking rod/bar system and a key and locking barrel with the central handle.
However, many electric roller doors are locked in various ways by different mechanisms which hold the roller curtain down firmly when closed. Unfortunately there are many roller doors sold in the UK which do not have any form of mechanism to lock and are not secure in any way, easily lifted from the floor, especially on single door sizes, which are not heavy.
The best roller garage doors for security are manufactured by SWS with their Seceuroglide range, all of which now have a form of mechanical locking in every model offered. The Seceuroglide Excel is the electric roller door developed, tested and certified with LPS1175 SR1 rating and is the result of many years of development in identifying the key weak points for attack and providing extra strength and unique locking methods.. SWS are known for their security window shutters and grilles so their background is security and this was key in the development of electric roller garage doors over the last 30 years.
A really cheap electric roller garage door will inevitably have no locking at all and the curtain is simply lowered and lifted by a rotating barrel, with variable connections to the top curtain slat, usually lightweight steel straps. When closed down these types of doors can be lifted quietly and easily from the bottom… Be aware!