The value of any gun is based on the make, model and condition, We need all 3 factors. You have given us none of the 3. No answer is possible without more information.
Let a gunsmith do it.
15m
15m
125 or so
Can't be answered without knowing who made it.
Yes, that would be the Model 51 made in 380 and 32 auto.
25-75 usd
50-5000 USD depending on EXACTLY what you have.
50-250 USD or so
the 380 is a 9mm short
Two different sizes. .32 is .320 inches in diameter, .380 is, well, .380. There are different .32 cartridges for revolvers and automatic pistols, the .380 is for automatic pistols. The .380 also has more power than a .32 auto.
If you don't have a manual, find a gunsmith and ask for help.