BTW just to clarify; very many (old, basic) microscopes are set up for (mainly biological) work with slides, i.e. using transmitted light (from below). The (rarer)alternative is a microscope that uses reflected light; if they have high magnification also, these are meant mainly for metallurgical work. BITD only a very few high magnification microscopes had the capability to use both reflected and/or transmitted light. [I am fortunate enough to own one; a Reichert 'Zetopan', but this is very much not a children's microscope.]
So a basic biological microscope has a lamp/mirror below the stage, and a stage that has a hole or a glass plate in it, to allow transmitted light work. Normally opaque materials, when sliced thin enough, can transmit enough light to allow good viewing this way.
When viewing something like a hair, you probably need to turn off the transmitted illumination and instead position a strong light source to the side of the stage, i.e. just above parallel to the stage.
cheers