Looked at your profile to see you are listed as male. In males, if you still have a prostate, you will usually feel some resistance when you pass the catheter through the prostate. It could be that you are not getting the catheter past the prostate and through the bladder neck into the bladder. The usual advice is to clean and lubricate. Then gently and slowly press the cath in. You will feel resistance at the prostate. Keep pressing, keep relaxing, maybe try a different angle or a slight twist, and you should feel the catheter pass through. At that point, urine will be released.
There aren't that many reasons you do not get any urine out. (1) You aren't producing any. That would not be good, and you'd be pretty sick pretty soon. I think you'd probably know something was wrong. If that's the case, get help. (2) You aren't getting the cath all the way into the bladder, because your technique needs improvement. (3) You can't pass the catheter in, because you've developed scar tissue (a stricture) in your urethra. (4) You need a smaller diameter catheter. So if you are using, say, a 14 french, switch to a 12. Maybe the thinner one will go in easier.
If you are having trouble getting past a stricture or your prostate, you might find some blood on the end of the catheter or the next time you void without a cath.
I can only think of two practical strategies. (1) Try searching youtube for nursing education videos. There used to be some there, and you can learn good technique from them. (2) Call your doc or if you haven't been able to void at all, go the ER. Sustained inability to void (say, over several hours) is a serious matter. You need to get it attended to.
Hope that helps and that you get the problem resolved quickly.
Best to you,
Brandi