How to setup a game for all phone resolutions?

Hello everybody,

I am a quite new unity game developer who likes to research a lot about unity and mobile gaming articles. I almost finished my final template before build & run and publish phases. However, I have a problem with different phone UI resolutions. I did a search on google but I only found Canvas solutions. I have no canvas object for now. And not really sure that I create it or not :S Here it is my hierarchy for now, which includes game files, objects, scripts under a sample scene.

Can you please tell me what I should do to fit my game for all resolutions? Create a canvas and move all files in it maybe? Not really sure.

Thanks for your help o/