Q:

How to warm up canned beans? 

A recipe is asking for "canned black beans, drained, rinsed and warmed".  
I've never just heated up beans by themselves.  How do I warm up these beans without using a microwave?  Do I heat them up in a pan with some butter/oil or in simmering water? 

A:

I'd use a microwave but you've ruled that out.  Taking "warmed" literally as meaning made warm but not hot, you could put them in a bowl, cover with boiling water and wait a few minutes.  I suspect that you actually want them hot, in which case you could put them in a small pan, pour over boiling water, cover, and return to the boil for a few minutes.  If you don't have an electric kettle, just boil a small pan of water and tip the beans in. 