There is no one size fits all description. Depending on exactly what you have, the procedures will vary. One thing that will be constant for any and all - MAKE SURE THE WEAPON IS UNLOADED!!!
You can request a owner's manual for free at the S&W web site.
Take it to a gunsmith and ask for help
shotgun, rifle and pistol.
Best to let a gunsmith show you how to disassemble the weapon.
No, the Mossberg 395 is a bolt action shotgun, NOT a semi-Automatic shotgun. It is a fine bolt action though.
Semiautomatic shotgun
50-500 usd
They were made in Japan by a firm called SKB.
100-300 USD
Follow the instructions in the owner's manual
Leave this to a trained gunsmith.
50-500 usd