How to obtain
1x Vines can be processed into 4 Twines each, or 1 Sinew will also be processed into 4 Twines at a time.
No crafting recipe has to be unlocked to process Vines and Sinews. You merely have to carry Vines or Sinews in your inventory or quickbar and then activate a Processor that has been placed into the game world by pointing the cursor at it and clicking your right mouse button or typing "f" (as the default key).
Then put the materials you want to process into the Processor with right-click on their icon that will now be sorted into the top category "processable" in the large window to the left side of the Processor window, or drag & drop the stack/s into the Processor slot with your left mouse button.
Vines often hang down from Wildwood-trees here and there in long strands. Vines can be collected without needing to equip a Power Cell.
Vines can also be obtained from all types of uncorrupted Leafies either when killing them and taking their Loot Bags or after taming and feeding them (optimally their exact favorite type of Food), after which you can harvest from your Pets by pulling them with your gauntlet.
Sinews can be obtained as a loot or even more often as a pet-harvest from nearly all Creatures in Creativerse except for seasonal event-specific spawns (like for Idol Events or Trog Trap Events) and Creatures spawned on Mob Spawners.
How to use
Twines are used as a material for crafts made in your Crafting Menu, mainly for Armor.
Twines cannot be put into any quickslots, cannot be consumed and cannot be placed into the Creativerse game worlds, different from blocks. They even cannot be put on display.