What is function of neurotransmitter

And also defined this . What is synapse

Neurotransmitter are molecules that convert electrical signals into chemical ones and transmit them from neurons to muscles or from one neuron to another.
Synapse is the junction of two connsecutive neurons. Signals from one neuron to another is transmitted through this synapse. It also ensures that the signals are transmitted only in one direction.

I hope you understood.