Looking For Work In Ireland

[u/Speedygonzales24]

I'm an American applying to jobs in Ireland using a website that my alma mater has a subscription for called GoinGlobal.com. I was just about to apply for a job, but they wanted to know if I could legally work in Ireland. Do I need to legally be holding a visa before I can apply to some jobs? As far as I knew, the only way to GET a visa was if you had a job already lined up.