There are multiple Bytes, each do different things. Bytes are sold at Lolbit's Byte store, located around the map.
The Gnat/Neon Bee/Neon Wasp: The first Bytes that you can buy. These will Damage Enemies. Pretty simple.
The Mini-Medpod/Medpod/Mega Medpod: These Bytes will heal you over-time. It's definitely worth buying the Mega Medpod, as it will probably be very helpful late in the game.
Mini Reaper/Reaper/X-Reaper: These Bytes have a chance of Insta-Killing Enemies. Again, Pretty simple.
Mini-FO/UFO/X-FO: These Bytes damage Enemies, just like the first Bytes you can get, except even the Mini-FO does more Damage than the Neon Wasp. WOW!
Block 5/Block 20/Block 50: These Bytes block the damage in their name. (If you bought Block20, it would block 20 Damage.) Again, Simple.
Pip-Pop/BOOM/KA-BOOM: These Bytes randomly explode for high damage to all enemies, they can only be used once per battle.
BossDrain-01/BossDrain-02/BossDrain-X: Drains HP of bosses.
Pearl: Heals the party, can be unlocked by getting five pearls in a row from Deedee's fishing minigame, the Pearl doesn't count towards your byte limit, just like the Fan so you can have more bytes than the byte limit.
Fan: Obtained after unlocking all 40 characters in update 1, after update 2 it can be obtained after unlocking all 48 characters. It boosts your party and shoots lasers at your enemies. You can also scream at it if you're nervous while battling Scott, Or Chipper's Revenge. Just like the Pearl, the Fan doesn't count towards your byte limit so you can have more than the byte limit.