Since you are clearly looking to learn Matlab, I would recommend you try implementing the code yourself. For a start though, understand that you could simulate an echo in the simplest sense as a delayed, and attenuated version of the original signal as mentioned in the prompt.
1) You can compute the delay in samples using the relation DelaySample = Fs*delay.
2) Create an 'impulse response' function with your original signal at the first sample, and the delayed impulse at a distance of DelaySample, and scaled by amp.
3) You can use a 1D convolution of the impulse response with the input signal in the time domain, or perform this calculation in the frequency domain, although you will need to take care of the zero-padding the output signal since the echo will be longer than the original signal.
I hope this helps!
