Translation:I see a dog.
"psa" is pronouced like "ps-a"?
No, the pronunciation isn't correct here.
It is just fluent psa
When use psa or pies?
Pies is the basic, Nominative form. "psa" is Accusative, which is probably the most widely used case. "widzieć" (to see) takes Accusative.
If you need more information about the cases, I'd recommend checking this topic for posts about cases.
lol, widze ps a
If psa is accusative, what then is piesem?
I have never encountered "piesem" before. Maybe you meant "psem"? That would be singular instrumental.
How about "I can see a dog" ?