You stay at least 5 metres away and you never touch them. What makes it better than it sounds is that the rule binds you, not the wildlife. If you sit still and a curious gentoo walks up to inspect your boot, that's the penguin's choice and you haven't broken anything. You just don't move toward it. Bird flu has tightened how strictly some of this is applied, so expect your guides to be firm about it.
Guides do enforce this, and they should. This isn't a petting zoo and the whole industry's licence to operate depends on visitors behaving. Expect to be corrected if you drift too close, and expect the team to reroute a walk around a resting seal rather than past it.
There's a related rule people trip over: you also give way. If an animal is crossing your path, you stop and let it through rather than walking around it.
You'll get the full IAATO briefing before your first landing, covering distances, behaviour and what's off limits.