Fluorescent lights have multiple parts. You have the tube, you have the ballast, and you have a starter. "Rapid start" tubes do not have an external starter however. If your light doesn't come on, it could be any of these components. But most likely it is the tube. That's why you replace the tube first. If that doesn't work, you'll have to move on to other things.
Note: Do not drop a fluorescent tube! They will shatter into dust (and that "dust" is glass with a coating on the inside). Quite a mess to clean up. And you sure don't want to get it in your eyes.
Second note: If you end up replacing a ballast, cover your flooring underneath the light with something protective. I have seen ballasts leak a black oily/tarry substance before. But that was over 40 years ago and I haven't seen it since. So either it's a rare occurrence, or newer ballasts are built differently and don't leak. Luckily that ballast I saw leak was over a tile floor, so the mess was clean-up-able (but a real mess doing so). If it had been over carpet, it would have mandated replacement of the carpet. Ballasts come in different wattages, depending on the length of the tube(s) in the fixture. But the folks at Home Depot and probably any hardware store can advise you what you need.
The contacts in the fixture that the tube mates with are often times really cheaply made. Over the years they crack. So inspect yours, and replace as needed.
If your problem is more than just the tube, consider replacing the entire fixture with a new LED fixture. Then you can forget about replacing bulbs/tubes for the rest of your life. If you go with LED, be sure and check the "color temperature" of the lights. LEDs can be so white that you feel like you're on the surface of the sun due to the harshness. The color temperature is rated numerically, the lower the number, the "warmer" (yellowish/reddish) the light is. The higher the number, the "cooler" (blue-ish) the light is. In a home you are going to want to stay below 4000K. 3500K is probably better in most peoples opinion. The incandescent lights of years past were very warm, about 2700K. You can get 5000K and 7000K LED lights. Don't. You will feel like you are in a commercial laboratory or hospital surgical suite. Fine for a garage workshop, not so good for looking at yourself in a mirror. I put 4000K in our kitchen and bathrooms. Honestly, I wish I had gone warmer. It took us quite a while to get used to even that level of white-ness.
One of our bathrooms has a fixture with six globe lights. Old - from the incandescent days. I initially replaced those bulbs with six 5000K 9watt LED bulbs. That's only 9x6 = 54 watts total. I thought it was going to be terribly dim in there. I turned those puppies on and I was blinded for a week. The cat nearly caught on fire and went running out. It was like the surface of the sun in there. I replaced them with 4000K globes and unscrewed half of them (now down to 27 watts). It's still mega-bright in there, but at least I no longer have to take special optical precautions before entry. 18-20 watts of 3500K would be about perfect, but I don't have that, so I continue living in my little tanning booth.