Yeah, vocals are a process that definitely require patience, when starting out.
To begin, I'll start with the compression question... Personally I would add next to no compression in the recording stage of your vocal chain. That doesn't mean that kissing the compressor ever so slightly may not actually help... The point is, keep any and all effects processing to a bare minimum in the recording stage of your vocals. The drier, the better... The key is to get the most natural sounding vocal recording possible... Then you can eq it, compress it, add delay or verb, etc.
Since you're using a USB Mic, I'm assuming that you're also not using a Mic pre amp. A pre amp can do just what its name states; amplify the vocal signal, BEFORE, it hits your daw (FL). Nonetheless, we all start somewhere, especially due to budget. Here are a couple steps to help you ensure a better vocal signal.
Right off the bat... Where is your input level hitting on your channel when recording your vocals? Imo, I would do my best to keep your vocal signal input peaking at around -6db on your vocal channel (when recording). Here's why... Higher quality mics coupled with higher quality Mic pre amps help ensure far less ground noise when recording vocals, among other types of tracking. In your case, using a USB direct to DAW microphone will require you to be a bit more attentive in the recording process, to ensure less ground and floor noise are present. That type of noise includes having your air conditioner on, the washer or dryer running upstairs, a faint buzz from a lamp in the room, etc. It's imperative for you to do some serious critical listening right now.
When you fire your Mic up for a sound check and get the levels hitting/peaking at around -6db; that's when you need do some critical listening in your head phones. What else are you hearing in your headphones coming from the microphone. Remember, the microphone is going to pick up everything when the Mic channel is on record... So make sure you do your best to get rid of every other sound in the room, and the entire house for that matter, when record is on... Again ground and floor noise. Everything to the fan of your laptop/desk top, to your AC being left on. The thing we have to remember is that when you turn your vocal up after recording it, you'll also be turning up everything else you recorded inadvertently as well... It's important to cut as much outside noise as possible.
If you've ensured that you don't have to compete with other noise sources while recording your vocals, now it's time to place your Mic in your room. I'm not sure of your setup, but do your best to keep your Mic away from the walls when recording... That equals less reflection in the recording process.
Do you have a wind screen / pop screen for your microphone? If not, I would most definitely invest in one... Even creating a poor man's version ( I've been there ) by using a wire hanger and some nylons can still do the trick. This will help ensure you receive a more natural recording when performing certain consonants such as T's, P's, or S's... It's a small adjustment, but again, very helpful.
I could've put this next step earlier... Mic placement from your face. Obviously you don't want to get too close nor too far away from the Mic when recording your vocals. This is going to take some experimenting on your part. Record some vocal takes and listen to the difference the recording sounds like when being 6 inches away from the Mic VS 3 inches away from the Mic. What Mic placement sounds better to you, will be up to you... Remember, no matter where you end up placing yourself in front of the microphone, try to keep healthy recording levels and low ground and floor noise like stated earlier.
The biggest misconception about recording vocals is that people think you can simply fix it after it's been recorded. Not true most of the time... Do your best to get the fattest, cleanest, and strongest signal on the way into your DAW... This mindset should be approached when recording any signal to your DAW.
After you've reached a vocal recording that's on par... Now you can add some processing in your DAW. Eq and compression are usually helpful, as well as verbs or delays... That's all to taste of course, and what the song itself is asking for... Limiting isn't a bad thing either... Just remember that less is more with vocal effect processing. Do your best to fix your vocal signal at the recording stage, not the post processing stage. Just my .02¢