Double slit for electrons (two beams or one)? I understand the double slit for waves but for electrons do we have a beam for each slit so each beam is responsible le to shoot electrons through its own slit. 
Or do we have just one beam? Which slit do we place the beam to? If it’s in the middle, wouldn’t all the electrons hit the wall between the two slits?
Sorry Ian very confused as how to carry out the experiment for electrons
 A: The distance between slits and the slits' width for the experiment are calculated to be smaller than the de Broglie wavelength of the electrons. (similar to the double slit for photons)
This allows to have  a double slit experiment with one electron at a time.

The interference effects show up in the probability distribution accumulated in the last slide.
So it is one beam with the appropriate DB wavelength for the geometry of the experiment to show the interference effects.
Edit after discussions in the comments:
this more recent experiment , found by Pieter, managed to create the double slit experiment as described by Feynman himself, electrons impinging on real slits.
A: The question is right to ask about how to do this in practice. Yes, this is done using two beams, but those beams come from the same source:

The electron beam (in a modified electron microscope) is sent through electron optics where it is split in two by a thin wire at negative voltage. After that the beams focused again at the same spot where it produces interference fringes. The electron optics works like a biprism.
In a way it is the same as a demonstration experiment that I show every year with a laser beam that is split in two by reflection from the front and the back of a thick glass plate. Those beams are then two centimeters apart. But when those beams are diverging (because of a lens in front of the laser) they will overlap at a large enough distance, where an interference pattern is then produced. It is is the pattern of interference from two point sources. The data from the electron experiment (shown in Anna V's answer) also look like that. A single-slit envelope pattern is not apparent.
Edit: I just came across this article with 600 eV electrons (50 pm wavelength) and real milled slits:"The individual slits are 62 nm wide and separated by 272 nm." 
Bach, Pope, Liou and Batelaan (2013)
A: This is not a direct answer to the question, because the question is built on some misconceptions:


*

*There's nothing special about "double slit" interferometry.  All that's required to produce interference fringes is for two waves from the same source to be superimposed at an angle.  This occurs in Young's double-slit interferometer, and it occurs in practically any other interferometer unless the two beams (from the same source) are perfectly superimposed (though interference still occurs in that case, it's more difficult to detect the interference).

*Two slits or two pinholes a small distance apart allow a single beam to be divided into two beams which spread out so that they overlap.  Something analogous happens with a single wire.  A diffraction grating can do the same thing.  The important thing is that two physically separated portions of the incoming beam be diverted in such a way that they overlap, with the path length differences between the two paths being less than the coherence length of the source light.
In more direct response to the question, there are many ways to prove electron interference.  Fabricating a sufficiently tiny version of Young's double slit, and finding a way to get a sufficiently coherent source of electrons is one way.  Another way would be to use diffraction in a crystal to generate two beam from one, then another crystal to combine the beams at a very small angle ( again, by diffraction).
A: There is only one source or one beam of electrons. They are directed toward the slits, with some hitting the middle and some making contact with the edges of the openings. 
A: In the Copenhagen interpretation, the principle is that there is a wave and that wave difracts through the holes like any other wave. The electron as a particle then appears at the screen with a probability that depends on the square magnitude of the wave. In this context, it is not suggested that the electron definitely went through one or other slit. Rather - if you adjust the experiment to determine which one it went through then you adjust the wave and so change the pattern on the screen. 
The interference of "particles" in quantum mechanics is, mathematically, the interference of some kind of waves. 
