Plutarch's purpose in writing was not so much to give a straightforward account of the actions or internal life of his subjects, as we might expect from a modern biographer, but to give character studies and moral examples. In his introduction to the lives of Aemilius Paullus and Timoleon, he says:

• I began the writing of my "Lives" for the sake of others, but I find that I am continuing the work and delighting in it now for my own sake also, using history as a mirror and endeavouring in a manner to fashion and adorn my life in conformity with the virtues therein depicted. For the result is like nothing else than daily living and associating together, when I receive and welcome each subject of my history in turn as my guest, so to speak, and observe carefully "how large he was and of what mien," and select from his career what is most important and most beautiful to know.
  ---
  But in my own case, the study of history and the familiarity with it which my writing produces, enables me, since I always cherish in my soul the records of the noblest and most estimable characters, to repel and put far from me whatever base, malicious, or ignoble suggestion my enforced associations may intrude upon me, calmly and dispassionately turning my thoughts away from them to the fairest of my examples.
  (Perrin translation)

Thus, for Plutarch, incidents that serve to demonstrate the character of his subject are far more interesting than the great battles or political struggles they took part in. As he says in the introduction to the lives of Alexander the Great and Julius Caesar:

• For it is not Histories that I am writing, but Lives; and in the most illustrious deeds there is not always a manifestation of virtue or vice, nay, a slight thing like a phrase or a jest often makes a greater revelation of character than battles when thousands fall, or the greatest armaments, or sieges of cities. Accordingly, just as painters get the likenesses in their portraits from the face and the expression of the eyes, wherein the character shows itself, but make very little account of the other parts of the body, so I must be permitted to devote myself rather to the signs of the soul in men, and by means of these to portray the life of each, leaving to others the description of their great contests.
  (Perrin translation)

The result is that Plutarch's biographies often focus on anecdotes about the subject, while omitting details of his (and it always is 'his') career that we would love to know.

Although the biographies are comparatively short (mostly between 20 and 30 pages long), Plutarch cannot resist digressions on anything that catches his interest. See, for example, the digression on the Athenians? treatment of retired beasts of burden in his life of Cato the Elder. Plutarch is also very interested in omens and frequently notes prodigious events, such as monstrous births, that preceded any great battle or the death of his subject.

The first translation into English of Plutarch's lives was by Sir Thomas North in 1579 (in fact a translation of the French translation of Jacques Amyot). This was the source Shakespeare used for his Roman plays: Coriolanus, Julius Caesar, and Antony and Cleopatra. It can be found online at Perseus.

John Dryden wrote a life of Plutarch to go with a translation of the lives by various translators published from 1683-1686. The translation was revised by Arthur Clough and re-issued in 1864. It can be found online at About Ancient/Classical History

The Loeb translation by Bernadotte Perrin was issued from 1914. The Roman lives, and some of the Greek lives can be found here at Bill Thayer's Lacus Curtius. Some more of the Greek lives can be found at Perseus.