Samuel Pepys was a man of somewhat humble beginning (his father had been a tailor), but he also had family in the British government, and family that had gone to Cambridge (Pepys himself graduated from Cambridge) and these connections and this education provided him an entry into the Admiralty where Pepys spent much of his working life. As a clerk in the Admiralty, Pepys proved to be a capable administrator, instrumental in the growing efforts to make the British Navy more professional. In fact, Pepys’ personal efforts helped develop the British Navy into the great force it would become in later years.
He was a man well versed in the literature and the intellectual pursuits of his time. Having graduated from Cambridge University, he continued academic interests into his post-collegiate life, even becoming a member of the Royal Society in his later life; in addition, he was a life-long devotee of the theatre – so much so, that, at several points in his diary, he vows to spend less time at the theatre (especially on lighter fare), as he feels such activity keeps him from more serious pursuits, but it’s not long before he has slipped back again into his theater-going habit.
He was quite capable in accounting (largely self-taught) and in the technical aspects of Naval ships, armaments, and the Naval bureaucracy (again, largely self-taught, though with generous help from others in the Admiralty whom he sought out) and proved himself a most capable administrator.
He is best known for a diary  which he kept from January 1, 1660 through May 31, 1669. This diary is perhaps the most famous diary in English. Its fame is due, in part, to Pepys’ position as a middle-manager in the British government during the Restoration; as a result, we get a lot of first-hand information about the workings of the government of that time, and to the important events which Pepys narrates as an eyewitness – the restoration of Charles II as king in 1660, the Second Dutch War of 1665-1667 (which the British lost), the Great Plague of 1664-65 and the Great Fire of London in 1666, which destroyed a large part of the city, though Pepys’ house escaped.
Pepys makes plenty of personal observations of his colleagues in government, some quite astute, others rather petty, and Pepys keeps a fairly detailed record of his romantic adventures (some of it bordering on sexual harassment, and some of it clearly harassment) with serving girls and some married women in his circle, and from the lower classes. Pepys never intended his diary for public consumption, and he even wrote the diary in coded shorthand, which was not fully decoded until the late 19th c. He also used French, Spanish, and Latin words and phrases (coded as well) to describe the more salacious elements of his sexual adventures, again with the idea of keeping prying eyes from learning much.
When he thought that keeping the diary (which he generally did late at night in poor lighting) was ruining his eyesight, he gave it up. In fact, he gave up writing altogether, choosing to dictate all matters relating to his work; as he could not trust private matters and observations such as he entrusts to his diary to the discretion of his secretaries, he gave up the diary altogether. Pepys had a good long career after 1669, being elected to Parliament, and also becoming a member of the Royal Society which he served in an official capacity.
Reading the whole diary  (it usually comes to 9 or 10 volumes, roughly one per year) is a daunting task, and it will likely provide more information than you ever imagined anyone would want about 17th c. England (my apologies to the handful of Restoration scholars and British Naval historians in the KC Metro). There are, however, abridged editions , which collapse the whole diary into a single volume, such as The Shorter Pepys , edited by Robert Latham. There is even (you might have to look high and low for this) a nice audiobook abridgment of the Diary read by Kenneth Brannagh.
Pepys writes in a rather simple but clear style – but, as this was not a work intended for public consumption, or even for the eyes of his friends, it is not written in a more formal style. For me, the fact that the work was not intended for other eyes, and yet still provides such a wealth of detail about the personal and professional life of a man, consistently set down at night or in the early morning – that makes the work compelling. For we get a wonderful view of a man determined to figure out his world, even as he tried to make his way in that world, and we get a very honest picture of his struggle to make his way and to grow and of the man himself, warts and all. For me, that’s a good reason to take a crack at Pepys.