I too am new to 3D, but my son who has used the printer I now have, a Prusa, tells me that putting filament parts in a box with a saucer of acetone will "ploish" the filament I have. It is apparently dependant on the variety of filament you are using.
The Prusa handbook suggests some sort of superglue (CA) for joining parts. The slicer I am using comes up with warnings about corners and such, there's a tick box to hit which blends and softens them too, maybe only that slicer?
Remember I am totally new to this, less than a week so I am possibly talking rubbish again.

As I was having issues printing a piece my son had designed I went back to instructions. I am using PETG filament, previous jobs have gone well.
I have just tired again, upped the nozzle temp to 240 and cleaned the bed properly, no issues.
It seems that not being diligent on cleaning the bed was the issue, so therefore, Mea Culpa!

Acetone smoothing only works on ABS, with PLA or PETG you are using filler of some sort and wet n dry. When you have adhesion issues with the bed use cheap hair spray.

I generally use PLA or occasionally PETG.

I find the brand of filament makes quite a difference to the results.  My favourite at the moment is Creality Hyper Series which I buy when they have one of their frequent sales.

For smoothing, I typically knock back any lumps with 80 grit and soften  edges etc with 240.  I paint with a primer and then sand the whole thing “across the grain” focusing on any bits that I care about how they look.  Then paint and flatten with 400 grit until I’ve got the surface I want.  A layer of colour, flatten, final coat of colour.

Orientation of the part when printing makes a difference but you’ll have to experiment with that.  Similarly, tweaking the gap between any support material and the part can make for a much cleaner removal of supports.  Part design, orientation and even printing a component in multiple sections that you then glue together are all useful techniques.

Scraping with a wood scraper can work on some surfaces.

I’m about to experiment with Methyl Acetate on PLA as a chemical smoother.  This can also strengthen the part by bonding the surface better, but without losing too much detail….or so I’m told.

Hope that helps.