where to start is with some books on process of reloading and a good mentor if you can find one . after that gather the equipment and components required .
Just do a Goggle search for reloading manuals . All the major manufactures produce them for sale. Or you can always try a used book store . or ebay for used ones.
If you're in a bigger town or city a trip to the local library might be a good place to start. Most medium and bigger libraries will have a firearms section with a couple or more reloading books.
With your stated goal of starting with rifle rounds a good option would be one of the Lee single stage kits that comes with priming tool and scale. And a set of the 8mm Mauser dies of course. You'll end up replacing some of the items in due time. But for now you get all you need to start out and load usable ammo.
As for buying a manual I'd suggest that a good place to start is the Lyman reloading manual. Currently in its 50th printing. My 49th Edition has a little over 100 pages before the reloading data on how to set up and good practices for reloading.
As for where to buy components and powder? At this point with the market being tight I'd say keep your eyes open and pick up what you need wherever you find it. Some of the Canadian Tire stores have a stronger focus on hunting and shooting and stock bullets, primers and powder if you can't find any at the local gun stores. And don't be shocked at prices. You're picking a nasty time to get started with all the prices being at an all time high. But then ammo has gone up by a lot too! It's all relative I guess.
As someone new to the hobby, I second the recommendation about a book first - and Lyman 49 or 50 is excellent start. Realize there are likely over 100 powders available - maybe some 8 or 10 of them are suitable for your 8x57 - probably two or three are "best". So just buying a random container of powder without a bit of background can be very waste of time and money. You will likely want Large Rifle primers - but sometimes need Large Rifle Magnum primers for certain powders or uses - refer to a book!!! Commercial cases that you have previously fired in your rifle are likely about perfect to start. Is reasonable to expect to get 6 to 10 "reloads" from a piece of brass - sometimes a lot more, sometimes a lot less - again, a good reference book will help explain that.
The main issue with relying solely on a "mentor" is that many dudes have hand loaded for years - doing the same thing over and over, and have never read a book. So sometimes they are an assist, but sometimes get you headed off where you do not really want to go...
You will find some association among producers - so the Lyman book is often showing how to do with Lyman tools. A Speer book is showing how to do same thing with RCBS tools. Lee book = Lee tools. Same with Hornady. But a great deal of mix and match is often possible - can easily use Hornady dies in an RCBS press and a Lee shell holder, for example.
At the beginning, your objective is to get rounds to go "bang" every time, and with even a bit of care, will be "as good as" most factory stuff. As you progress, can get more fussy about the results that you desire to get. Try not to get caught in the "trap" of bench rest and long range shooters - they often use specialized hand loading techniques - especially in their brass preparation - often in very expensive custom rifles - that will usually make no difference in most store bought guns.
It might be helpful do search on YouTube as well as they have some decent videos on reloading .
I started to reload with a very basic Lee kit - pound the cases into a die - pound them out - used a scoop to measure and dispense powder. The rounds went "bang", but several issues - for most people, biggest is that the process only neck sized that brass - so brass fired in someone else's rifle likely would not fit into yours. Got me started, but also motivated me to move up to a press and full length sizing. Then to using a scale to actually weigh the powder. And so on. A good mentor could coach you to a set of tooling that will last you for your reloading life time - or at least until you get the next "desire". Buying used stuff, I suspect that you should plan to spend $300 or so to equip yourself. For comparison, the automated powder dispenser that I received a couple weeks ago was about $407 mailed to me from Amazon.ca. So much for "savings" by reloading...