1) An electron source (ex. a cathode) sends electrons downward from the 
top 
of the transmission electron microscope (TEM).  Solenoids and/or an 
area of 
positive charge at the bottom of the TEM focus and accelerate the beam 
downward.  (Down is a good direction so gravity is not an obstacle.)

2) Electrons pass through the grid and specimen, but some electrons are 
stopped by the "opaque" parts of the specimen, which has been stained 
with 
phosphotungstic acid for this effect.  Usually, specimens are too 
permeable 
to electrons without acid and so would not produce a good image.  The 
result 
is a negative image of the specimen.

3) After the beam hits the specimen and grid, it spreads out (the image 
is 
magnified) until it hits a stage at the bottom of the TEM tube; the 
stage is 
coated with a substance that fluoresces when hit with a charged 
particle, so 
the electrons that passed through the more translucent parts of the 
specimen 
help form an image  on the stage.

4) This image can be further magnified by a modified simple light 
microscope, whose light source is the stage itself.  A camera is also attached.