As the name implies, the focus of "Junk" monsters is utilizing lower Level monsters to build powerful Synchro Monsters. "Junk" monsters are usually used with monsters with low Levels to use as Synchro Material Monsters. One familiar combo is using "Junk Synchron" to Special Summon Level 2 or lower monsters such as "Speed Warrior" and "Quillbolt Hedgehog" from the Graveyard in preparation for Synchro Summons, especially "Junk Warrior", which gains ATK equal to the combined ATK of all Level 2 or lower monsters you control. Using many low Level monsters also helps when Synchro Summoning "Junk Destroyer" by maximizing its ability to destroy cards on the field. "Junk Archer" can banish a monster until the End Phase, enabling your monsters to attack without worrying about a high ATK monster. "Junk Gardna" and "Junk Defender" serve as great ways to stall for time when you can't pull out your better combos. When running low on Synchro Monsters to use you can still get help from your "Junk" monsters by banishing them using the effects of "Junk Blader" and "Junk Berserker". The effect of "Junk Sychron" can make use of "Doppelwarrior" (it will Special Summon itself from your hand when you Special Summon a monster from your Graveyard and it can give you two tokens when you use it for a Synchro Summon). For example, you could Special Summon a Level 2 Tuner from your Graveyard and Special Summon "Doppelwarrior" from your hand. Then you can Synchro Summon "Armory Arm" and get two tokens. Tune a token and "Armory Arm" with "Junk Synchron" to Synchro Summon a Level 8 monster.
While fast and very proficient in swarming the field, Junk monsters often lack raw attack power: none of them go above 2700. As such, the Junk archetype is very reliant on using their effects to their fullest potential to gain an advantage. As such, cards that negate effects are a serious problem for a Junk deck, as they're forced to rely on their sub-par attack power. This is even more prevalent for the non-Synchro members of the archetype, all of which are almost purely based on getting monsters out on the field for fast Synchro summons. Because of this cards like Discord severely restrict the Junk archetype.