@southjock the way I think of it is like any other exercise; like when I first started doing yoga I couldn't stretch my hamstrings completely and I couldn't hold the position for very long without discomfort. The more I worked it out the easier it got.
It's not so much that you're making your hole "looser" per se but stretching it a la hamstrings, and in the process you'll be developing more strength and control.
I have a couple small toys I use on a regular basis including a small buttplug and a vibrator. They aren't "sex" toys per se (I mean, they are, but I don't (just) use them to masturbate lol), they're more like my pushup handles or foam roller. Using those will get you used to stretching and opening up, plus you'll learn a better understanding of your internal goings-on, and it feels fantastic. They aren't meant to mimic a cock per se - I'd use a different toy for that lol - but rather to workout your hole.
What you'll find over time (and faster than you think) is that not only are you going to be able to relax and stretch to take cock with ease, but considerably less pain. There will almost always be some mild pain when a guy first pushes into you, but it's the kind of sensation and typically (for me and probably a lot of bottoms) results in an excited intake of breath because it's also extremely pleasurable.
Also keep in mind that your comfort (or discomfort) has as much (or even more) to do with the top as you training your hole.
Hope this helps, and feel free to PM me if you have any questions as you begin this awesome journey!