Reeds, mouthpiece and clarinet are equipment issues that we all do our best with. I think so, and they are being played at this very moment by a herd of wild unicorns. In other words, despite the fact that you may have heard a player perform with a beautiful tone and flawless intonation, that player was probably just as frustrated with the reed, mouthpiece, and instrument as you are with yours. Do the best you can with equipment. But, good intonation begins and ends between the ears.
Tuners have two basic functions.
The first is 'hearing' a pitch and indicating how close that pitch is to the tempered ideal. Both functions are vital for practicing, and most contemporary tuners do both. Most tuners also have a calibration setting that allows you to use A440 as your tuning standard, or a range of several hertz either higher or lower. Online Beyond that, tuners come in many shapes, sizes, and prices. I use one made by Korg called the AT-1.