OTG creates a link between your mobile phone and other computer peripherals such as USB flash drive, mouse, keyboard, game pad, card reader, external hard-drive etc.
it is plug and play, no need of any set-up.
it is mostly compatible with android phones.
Now you don't essentially need a laptop to view what is stored in your flash or external hard-drive. you can do it ON-THE-Go.
It can works well with all Android devices WITH custom ROM/Kernel that support USB Host mode.
this is a list of some of the Popular Compatible Device:
Google: Nexus 5 / 6 / 7 / 9 / 10
Samsung: Galaxy S2 S3 S4 S5 Note 2 3 | Galaxy Note 8.0 Galaxy Note 10.1 2014 Edition | Galaxy Tab 3 8.0 10.1 | Galaxy Note pro 12.2, Tab pro 12.2 / 10.1 / 8.4 | Galaxy Tab S 8.4 / 10.5 / 13.3
Motorola: Moto G Phone | Xoom Tablet
HTC: HTC One M7 M8
Nokia: Lumia 2520 Tablet | Nokia 603 | Asha 300 | C6-01 | C7 E6 E7 | N8
Toshiba: TG01 | encore
Tecno: F7/H7/R7/Phantom A+/Tablets
Tesco: HUDL 7" plus
Acer: Iconia B1-720 | B1-730 HD | A1-830 | A1-840 FHD A1-810 | W3-810 | Memo Pad HD 7 / 10
Lenove: Thinkpad 8 | IdeaTab A7-40, A7-30, A8-50, A10-7
LG: G3 G Pad 8.3 7.0 8.0 10.1
Sony: Xperia Z2 Miro/U/S/T/M/M2/SP/P/Z/Z1/Compact/Z2/Ultra/Z
Dell: Venue 7 / 8 / 8 Pro