Steve is right. You should avoid free hosting. Free hosting is always very slow. Site visitors will probably leave your site before it's even downloaded. Hosting can be had for about $1 per week, but if phpbb is completely new to you I understand your reticence at having to pay for hosting whilst you are still learning the software.
If you need to practice on phpbb, or if you want to learn how to use it before you pay for hosting, you should try hosting it on your own computer by installing free server software. If you are running Windows, search Google for a 'WAMP server', but if you are running a Linux computer you should search for a 'LAMP server'.
There is free WAMP software, and free instruction books on how to set up a WAMP server, Setting Up A WAMP Server On Your Windows Desktop
As the server will be on your own computer, nobody else will be able to access it, but you will be able to play with it for as long as you like and learn all about phpbb in your own environment. Once you are familiar with phpbb you would then be able to pay for hosting and create a phpbb site straight away.
The added bonus, once you have a WAMP server installed, is that you can then try out ANY free website software, and learn how it works.
You have also mentioned other boards. It is worth bearing in mind that phpbb is mobile friendly, but not every board is, and over 50% of web useres now access websites from a phone.