How is Camille Pissarro the same and different to Claude Monet?

That's a pretty enormous question. How are Madonna and Britney Spears the same and different? How shall I count the ways?

Monet is often credited with actually beginning impressionism (notably with his painting Impression Sunrise -- which by title and by style essentially gave birth to the artistic movement that would take on a similar name). However, Pissarro, 10 years Monet's senior, is often credited with the role of Father of impressionism. He receives this title mainly because of his age and the mentoring role he took among the close-knit group of incredibly famous impressionists and post-impressionsts (such as Monet, Renoir, Degas, Cezanne, Gauguin, Van Gogh, et cetera) with whom he exchanged a great many ideas on painting.

Monet and Pissarro were interested in similar things both stylistically and conceptually. The goal of the impressionist was to play with the effects of light, form, color, the changing seasons, the hours of the day, and so on. Mainly light. Monet largely painted landscapes, while Pissarro had the important distinction of being the only impressionist painter deeply interested in portraying French peasants (the country folk -- the hard working rural citizens). In contrast, Renoir, for example, was interested in portraying the bourgeois, second class, French citizens who were having a gay old time in the big cities.

There are litterally thousands upon thousands of differences between each impressionist (it would be a futile effort to even attempt to think of them all), and almost as many similarities.

Look at their body of work and their personal histories and you can rattle off a few hundred with no trouble.