HotS Talent: Raiders Recruitment

You gain 'stacks' (up to 50) for killing minions, mercs or heroes. It takes 15 stacks per mercenary recruitment, so you're limited to 3 recruits at any given times which will be displayed below the left-end of your mana bar. To consume the stacks, go to any non-boss mercenary camp and use it like most other targeted 'active' talents. Get close enough to the mercs so they're inside the talent's range (shown in yellow once talent is activated), then activate the skill on each merc; best to do this quickly as recruiting a merc will aggro the rest of the group and Raynor will also begin auto-attacking. The default key-mapping for all tier-1 talents is the '1' key. So, when you have enough stacks to recruit, get nearly withing melee-range of some mercs then press '1' and left-click on a merc, then press '1' again and left-click on another merc, then repeat again if necessary.

Bribe is a similar tier-1 talent available (so far) on to Azmodan, Brightwing, Falstad, Li-Li, Murky, and Nazeebo. It's also what Raynor used to have but he go this buffed (recruitment stacks lowered from 20 to 15) version in a post pre-release patch (unsure of patch # and date).

HTH