This is a short introduction to light-microscopy, illustrated with widefield microscopy. It introduces : - upright and inverted widefield microscopes - the transmitted and fluorescent light-path - contrasting methods (optical and at the sample level) - the molecular principle of fluorescence (Perrin-Jablonski) - objective, resolution and limitations of the method (diffraction, diffusion/scattering) In addition to the PPT (with few animations), a lighter PDF version is provided for preview in Zenodo. Illustrations are mostly extracted from the ThermoFisher Molecular Probes School of Fluorescence educator packet and from the course material from Micron Facility in Oxford. As stated in the presentation, illustrations are copyrighted but can be reproduced provided the original attribution is conserved.