You can choose between light signals or semaphore signals.
Block signalling or interlocking means the distance between two depots or stations tiled into blocks of same length.
The block length is the most problem onto model RRs in general.
The ideal Block length is the double to tripple length of your longest train but it works with shorter blocks of one and a half train length, too.
Normally block signals have their standard position aspect as clear with green light.
After a train entered the block, the block signal is being switched into stop position aspect with red light.
The prototypes using two closed blocks on red light for maximum safety, the before block of those in caution position aspect and the block before in clear position like the block before, too.
Normally a train runs from one free block into the next. Behind the train are two closed blocks and there before one block in caution with orange light.
If a faster train is running into a caution block it must breaking to stoo onto next following red signal.
Onto model RRs you can use one closed block there before a caution block and two clear blocks.
More easy block systems working with one closed block between two clear blocks.
Real interlocking systems working with one closed block or two closed blocks behind a train and one block in caution.
It is up to yourself what your coice would be.