I remember when I first started having Chinese lessons, my teacher used some Windows-based software to show me visualisations like these. It helped a lot to know where I was going wrong.

The visualisations here are the most useful part IMO, followed by the example sounds.

If you're a native English speaker learning Mandarin: one tip for the second tone is to make it sound like you're asking a question. In English, we raise the tone of the last syllable in a question. So if you pretend you're asking a question, you'll naturally get the right tone.