If you forget to charge your MacBook properly overnight, you can get headaches in the morning. And if you troubleshoot a broken MacBook, check if it can load. It is a way of excluding battery problems.
Older MacBooks have charging cable lights
If your MacBook was made before 2016 and has a magnetic charging cable (even the "old" L-shaped), it will have a light on the end of the cable indicating that it is charging. If the light is orange, load. If it is green, the battery is full and you release the AC adapter. Even if it is not turned on, it should still have light if the problem is not with the battery.
If you have a new MacBook with a USB type C charger, that's another story. The USB-C charger does not have the indicator light, which means that if your MacBook is not turned on, you will not know if the battery is the cause or if the cable is only broken.
If you have a really old cable or a third party you can miss the light as well.
One way to check when troubleshooting a USB C cable without light is to allow it to be plugged in for a while and check if the power strip gets hot. They generate heat while they are being charged, so if it is not charged, it will be cold.
Another thing you can try to shine a flashlight on the Apple logo on the back. If you can see something on the screen it means that your backlight is broken (a fairly common problem, often wrong because it doesn't get started at all) and you should find an Apple Store. Or maybe you have lowered the brightness all the way, and your MacBook is good.
Tip: Newer MacBooks make a sound when you connect the charger. It's one thing that sounds just like the sound when plugging in an iPhone, but it's quieter. You will also not hear whether the computer's sound is off or if the battery is completely dead when connecting the cable. You can still try to disconnect and reconnect the cable to listen to the sound. If you hear it, you know it's loaded.
Is it turned on, with the screen visible?
If so, the battery status is displayed in the top menu bar, along with apps with a lot of juice and alerts if your battery is old (and doesn't keep a charge very good). If the battery is charged, it will get a flash ball symbol over the battery icon.
If the icon is not displayed in the menu bar, it may be off. Open the System Settings app and click the "Energy Saver" icon as a lamp. The lower part should be "Show battery status in the menu bar." Make sure this is highlighted.
You can also adjust other power related settings from here, including how quickly your display turns off when not in use.
If all this fails and you're still having trouble with a busted MacBook, it's best to contact your local Apple Store for repairs.