how to wait for first command to finish?

Shell scripts, no matter how they are executed, execute one command after the other. So your code will execute results.sh after the last command of st_new.sh has finished.

Now there is a special command which messes this up: &

cmd &

means: “Start a new background process and execute cmd in it. After starting the background process, immediately continue with the next command in the script.”

That means & doesn’t wait for cmd to do it’s work. My guess is that st_new.sh contains such a command. If that is the case, then you need to modify the script:

cmd &
BACK_PID=$!

This puts the process ID (PID) of the new background process in the variable BACK_PID. You can then wait for it to end:

while kill -0 $BACK_PID ; do
    echo "Process is still active..."
    sleep 1
    # You can add a timeout here if you want
done

or, if you don’t want any special handling/output simply

wait $BACK_PID

Note that some programs automatically start a background process when you run them, even if you omit the &. Check the documentation, they often have an option to write their PID to a file or you can run them in the foreground with an option and then use the shell’s & command instead to get the PID.