Dynamic singers are a gift and a mixing problem. The soft lines disappear under the band, the big lines jump out of the speakers, and you end up doing fader aerobics for three and a half minutes. I did this for years with a mouse before accepting what every engineer since the 1960s already knew: this is what a compressor is for.
A compressor is an automatic volume hand. When the signal crosses a line you set, it pulls the level down; when the signal drops back under, it lets go. That's the whole machine. Everything else is deciding where the line is and how fast the hand moves.
On the vocal track
Drag Compressor from Audio Effects onto the vocal. The knobs that matter, in the order I actually set them:
Threshold. The line. Pull it down until the gain-reduction meter shows movement on the loud lines and nothing on the quiet ones. For a jumpy vocal you'll typically land somewhere that gives 3-6 dB of reduction on the shouty parts. If the meter never rests, the threshold is too low - you're compressing everything, which is the same as compressing nothing.
Ratio. How hard the hand pushes. 3:1 or 4:1 is the vocal neighborhood. The default here is 4:1 and honestly I rarely move it.
Attack. How fast the hand grabs. 5-15 ms on a vocal - fast enough to catch a syllable, slow enough that the front of each word still pokes through. If the vocal starts sounding blunted and lispless, your attack is too fast.
Release. How fast it lets go. Somewhere around 100-250 ms, or until the meter breathes with the phrases instead of fluttering on every word. Fluttering release is the number one "something sounds weird and I can't say what" culprit.
Makeup. Compression makes things quieter, so there's makeup gain to bring the level back - or flip on auto makeup and let it do the bookkeeping. One warning: louder sounds better to human ears, always. When you A/B the compressor on and off, match the levels first, otherwise "on" wins every comparison for the wrong reason.
What it should sound like
Ideally, not like anything. Play the whole song. The quiet lines should now sit where you can hear the words without leaning in, the loud lines should stay in the picture instead of leaping out of it, and if a stranger asked what you changed, "the singer got more consistent" is the right answer. Pumping, breathing, audible grabbing - all signs to raise the threshold or slow the release.
Don't stack it with the Glue on the master expecting double the effect, either - they're doing different jobs. The track compressor evens out one performance; the bus compressor makes the band move together. A vocal that's already even gives the bus compressor less to overreact to, which is why the order is: fix the track first.