mkfifo create a named pipe. Opening a FIFO for reading normally blocks until some other process opens the same FIFO for writing, and vice versa.

You need two shell.

Create the fifo

mkfifo /tmp/fifo1

Try to read from the fifo will block until we write inside

cat /tmp/fifo1

In the second shell write something in the fifo

echo "Hello fifo" > /tmp/fifo1

The cat from the first shell should have write Hello fifo