There isn't much of Lestrade in The Hound of the Baskervilles. Lestrade's a policeman from Scotland Yard; he and Holmes frequently clash over whether Holmes' creative deductions are believable or not. In fact, he's a longtime frenemy of Holmes dating all the way back to the first Holmes adventure A Study in Scarlet. But apparently, by The Hound of the Baskervilles, they've mostly settled their differences.
Holmes sends for Lestrade to come down to Dartmoor when he's ready to ambush Stapleton so they can have an official cop on hand to arrest him. But other than getting off the train at Coombe Tracey, Lestrade doesn't do much else in this book; all Watson says is that he sees "at once from the reverential way in which Lestrade gazed at [his] companion [Holmes] that he had learned a good deal since the days when they first worked together" (13.138).
While Lestrade is technically present when Holmes and Watson go to ambush Stapleton, he doesn't have to arrest anyone thanks to Stapleton's plunge into the Grimpen Mire. The fact that he appears at all seems to be a kind of fan service to devoted readers of the Holmes stories, to reassure us that Lestrade is still working with Holmes on his adventures.