I'm a mental health first aider. The idea is that I'm on hand, in the moment. I can then refer elsewhere, give information/ contact details, offer advice, check back later on...
For some that's better than having to find time to call their GP, hope the receptionist will allow a telephone appointment, wait for a call back (can't be in work hours as we're not allowed our phones on us) or take time off for a face to face appointment, and so on.
It helps that I know my colleagues, they're not strangers to me, I can spot when they don't seem themselves, I might know about an event in their lives that may mean they'll benefit from my help.
My role is also to advocate for well being within the workplace, anything that might help support good mental health, even down to making the staff room comfortable.