The voice is an organic instrument. Your body is your voice. Just as a long distance runner needs to do a warm-up walk/jog and stretch before a race or extended run, so do we dedicated singers need to warm-up our voices before performing. Otherwise, we risk strain or injury – the same as for the runner.
One of my favorites is to start with an easy hum (on an “NG” sound) through the first five notes of a scale and back down. The goal is to keep the chords connected and making a clear sound throughout. It’s important to have a comfortable volume in my warm-ups rather than trying to be loud. Keeping the chords connected and the breath flow constant is important to get everything loosened up and ready to perform.
Another excellent exercise for vocal warm-ups is the lip bubble (also called lip roll) and/or tongue trill. This is another exercise I do every day to help loosen up the chords and get everything relaxed so that singing is effortless. You can Google the names of these exercises to find several useful YouTube videos that illustrate how these exercises are supposed to sound.
I recommend working with a teacher to ensure that you are doing these exercises correctly. It’s also good to to have a teacher help determine the best warm-up strategy for you. There are many options!