If you are just dipping your toe into the water, you will probably do fine just winging it. If your amp has a standby switch for the power tubes, it's best to employ that to run new tubes in for a while before putting the amp in operate mode. That said, such products are not the majority. Also certain products do better with a bad tube than others. Personally, I don't really know why more amps don't fail gracefully when dealing with a bad tube. But again, lets presume happy path, you'll likely do fine.
You may want to sniff around your local area to find out if you actually can get someone to test your tubes. Audio groups, guitar amplifier techs / guitar shops, and even putting an ad on Craigslist will likely turn something up so long as you're reasonably close to civilization.
At some point, if you find yourself deep enough into tubes, you will push yourself into buying a tube tester. By that I mean, you'll be buying and trying tubes on a level that justifies the investment more than not having it. It's not as painful as it sounds. There are a few new production items that offer decent performance and cost, check the guitar focused solutions. Really, in this age, it makes too much sense to offer a software based solution that employs minimal and relatively low cost hardware all at a very attainable price. I think those do exist on some level whenever I look into it, but I feel they should be far more ubiquitous
