Having trouble getting started in making a decent sound. Can anyone help me? Thanks.

cf

You're blowing in the wrong end of the horn!!!
Seriously, without seeing or hearing you play, and with so little info from you, there isn't much anyone can do for you. Consider posting a recording, or better yet a video, tell us what you want to fix and maybe we can give you something useful.
Best advice I can give, is spend some time with a competent private teacher. There really is no substitute.

Yes, I'm afraid Steve is right. Get a teacher. Forums can only help so much.

As stated above your particular question has too many variables to be able able to answer properly. Possibilites that lead to not getting a good and decent tone can be . . . .

Your aren't pushing enough air through the isntrument.
You are trying too hard and pushing too much air.
You lips are too tight or your lips are too loose.
Your method of support may be incorrect.
Your posture could be contributing to a poor embouchre.
Are you trying to play Einsatz or Ansatz?
The mouthpiece is being placed too high on your lips.
The mouthpiece is being placed too low on your lips.
Your mouthpiece angle is too high, or your mouthpiece angle is too low, or it's too far off to the side, or it's too acute or too obtuse.
It could be that mouthpiece is meant for a different lead pipe/tube and doesn't fit correctly. Or it could be your slide is not in a good position for the partial you are trying to play. If your trombone has a trigger, the valve may not be aligned correctly.
Depending on the quality of the instrument you may be constrained to a certain quality of tone. When was the last time the instrument was cleaned properly?

You see?