Since you are "totally new", I will add a bit to what OM said.

A trail runner, in case you did not know, is billed as a running shoe and also built like one, but a good trail runner has a tread that is designed to be much knobbier so it can grip uneven or slick surfaces better. It should also be a bit more rugged to withstand more abuse. Regular running shoes are built for tracks or streets, not trails.

The differences in fit from one shoe company to another is based on how each company views the "ideal" foot. Because everyone's feet are unique to some degree, there is no "ideal" way to build a shoe. Some feet are wider, some taller, some have stubby toes, others lengthy toes ... well, you get the idea.

So, you just have to try on a variety of shoes in the same size from different makers. It helps if you can wear them around the house for a couple of days and return them in like-new condition, if things don't feel right. Ask about returns before you buy. Wear the same socks you would wear on the trail, too.

You don't need a pair of massive boots on your feet in order to hike. They don't have to be all leather or built for mountain climbing. If the salesperson tells you this, ignore them. Lightweight shoes or boots don't last forever, but they are more pleasant to hike in and you expend less energy over the course of many miles.

I hope this helps.