General ⇒ Confusion over reference coordinates using \put()

[lilyo]

Hello,

I am making a presentation with beamer. I want to put three figures next to each other on a slide with text above and underneath each one.
I'm using columns. Using \includegraphics is not working the way I want it to, as there is always a huge left margin mucking up the symmetry.
So I'm using \put.

But I am unable to figure out what coordinates to use; despite much trial and error my picture fails t display.
In:
\begin{picture}(a,b)(x,y)

I have figured out that (a,b) refer to length in x, lenth in y of the picture.
Changing (x,y) has no effect.

\put(x1,y1)

Now what is the zero coordinate to which x1 and y1 refer?

I have tried all sorts of values for x1 and y1 ranging from ±0.5 to ±500 and no joy.

Any help much appreciated

Lily