Consider the circuit diagram containing two NOR gates. You realize it has two outputs Q and Q', which can take two states...
A bistable multivibrator switches back and forth between the two states (hence the part bi-). Has the multivibrator found a result, it remains stable. Only by using the inputs R and S you switch the multivibrator. This behaviour applies to all latches and flip-flops.
With the circuit shown, it becomes more evident how it works...
When you connect the battery, either Q or Q' lights up. This is determined by chance.
After that you can switch between the two results by using R and S. Try this out to understand its behaviour.
This is already the first latch you built.