Checking voltage at an outlet is very easy however you want to use the right tester and a good at that.
Digital is mainly what you’ll be using. If checking a 120-volt outlet just to see if you have power and if it’s wired correctly you will want to use a socket tester this type of tester will show you if you have power and if the wires were installed the correct way. If you find adjacent outlets are also wired incorrectly you may want to check the source in the panel. Meaning, if it’s wired wrong in the panel that the whole circuit will be wrong.
Non-Contact testers are good for maybe a quick reference to see if the line has power but can give you false readings. So use this type with caution. Non-Contact testers can even beep if you move it too fast against your own skin
Two Range Tester. These are good and again for a quick reading. If you only have 120-volts only half will light up indicating just 120-volts. But if you have 220-volts both ends light up. This is very helpful if you’re testing wires for power and think you’re only going to have 120 volts and find out you’re on two hot leads and find yourself with 220-volts instead. Two Range Tester
Multi-Meters These is by far the best way to test for power and can be used for many other projects. Yes, they can seem a bit more complicated over other testers but yet once you know the correct setting they will provide you a much better reading. The question is, do you need one. Here is a decent multimeter and easy on the pocket.