In case you want to read the most famous pages in Proust's In Search of Lost Time without reading the whole stuff, go straightly to page 50 or 70 or the first volume, Swann's Way.
There the narrator explains that, one day, long after the events in the novel happened, he was soaking a madeleine into a cup of tea when the taste and odor made him remember the old days, when he was a child and his aunt let him eat madeleines soaked into tea. This sensation also produced a great joy in his mind, because this kind of epiphany is what, for Proust, can lead to happiness.
There are actually three of four other key moments that have just the same importance in In Search of Lost Time. The author will summarize, study and understand these moments in the last volume, when, during a new revelation, he puts all the pieces of his sensations together and decides to make a book out of them.