I am an Andriod user. How can I tell if somebody touches my phone?
Your question is vague - perhaps check the recently opened apps screen to see if any app that you haven't used yourself was opened?
If your android phone has front facing camera,then you can use Hidden Eye app to know who did it.It also has pro version with much more features which you might be interested in.But try the free version first to check whether it works for you or not.
Check for fingerprints.
I'm sorry but your question is very vague. I assume you mean "How can you tell if someone used your phone."