Sting made his WWE debut at Wrestlemania 31 in a loss to HHH.
He will be making his second WWE match appearace this year at Summerslam 2015 in Brooklyn, NY. Sting is included in the advertising and marketing materials for the show, and is expected to return to WWE TV as soon as tonight at Battleground or tomorrow on Raw.
WWE officials, most notably Vince McMahon and HHH, were not impressed by Sting at Wrestlemania, and Sting is said to be motivated to improve his reputation.
At this point, Sting is scheduled for a match against Bray Wyatt at Summerslam 2015. While there are rumors that he could be facing the Undertaker, it seems more likely that Taker is headed for Brock Lesnar and Sting would be in a separate match.
Given that Sting lost his first match, it seems likely that WWE would have him win this match, to set up more matches down the line, at least for one at Wrestlemania 32.
There are reports that Luke Harper (and the injured Erick Rowan) would be returning to the Wyatt family, so the match with Sting could potentitally be a multiple man tag match or handicap match as well.