Knowing the model would help a little, but in general, you field strip it, put some solvent on it, let it sit a few minutes, wipe the solvent off, lube it, reassemble it. That's a very basic description.
A Smith and Wesson M&P 40 is a .40 caliber hand gun.
No
Used, maybe $200 tops.
250 or so
Smith and Wesson. It's the manufacturer who developed the caliber, a frequent practice in the firearm industry.
300-525 USD
Go to S&W's web site and request a owner's manual.
Ask a gunsmith for assistancee.
When referring to the .40 caliber cartridge, SW always stands for Smith and Wesson, regardless of the brand of the gun, because the .40 S&W cartridge was designed by Smith and Wesson. The offical name of the cartridge is .40 S&W, just like the official name of the .45 is .45 ACP (Automatic Colt Pistol). People have a habit of leaving off things they don't think are important, so the .40 S&W is commonly called just "40."
Best to have a gunsmith show you or contact S&W and ask for an owners manual.
If you go to S&W's website you can get a manual for free.
Call S&W and they will send you an owner's manual for free. Go to the S&W website and you can download one for free. Find a gunsmith and ask for help.