Go to the PSN store and use the PSDLE tool select the option to output a download link, export to a csv file, and copy/paste the download link into a browser while you're logged into your PSN account. Insert your PS2 disc into any standard DVD-R or DVD-RW drive and use imgburn to dump the game to a file. PS3: Dump games from a modded PS3 system or with a compatible Blu-Ray Drivestraight to your PC
Once modded install cleanrip to the homebrew channel and dump the game to a flash drive or SD card.
Wii: in order to dump Wii games you will either need to mod a Wii or the Wii portion of a WiiU (the process is the same on both). WiiU: in order to dump a game you will need a modded WiiU and then software like the DDD WiiU title dumper This isn't a dedicated system modding thread so the information I'm leaving here is extremely basic and only based on my limited knowledge of the systems I myself have ripped games for or have researched ripping games for. There is no other legal way to obtain a ROM and it is not legal to download a ROM of a game you already own. Keep in mind in order to legally run a game through an emulator you will need to rip it yourself. I don't have access to a non-windows PC device so feel free to let me know your favorites This section will be for emulators that work in other operating systems. Sega Naomi, Naomi 2, Atomiswave Emulation: DEmul Sega Model 2 Emulation: Elsemi's Model 2 Emulator GB, GBC, GBA Emulation: MGBA/ Visual Boy Advance Vita Emulation: Vita 3K(barely working state) Master System, Game Gear, Genesis/Megadrive, SegaCD/MegaCD, 32X Emulation: Kega Fusion PSX Emulation: BeetleHW(Mednafen fork)/ Mednafen(better experience with BIOS) PS2 Emulation: PCSX2 (requires ripped BIOS) Xbox 360 Emulation: (some games working, high system requirements.) So no need to fret if you're favorite emulator is not listed. There are multiple viable emulators for many systems but as this is aimed at being a general purpose beginners guide the ones linked are as far as I'm aware are the best option for their respective systems. In order to emulate games you'll need an actual emulator.