Shabbos 12:2-3

Shabbos 12:2

One is liable for plowing, weeding, or cutting or trimming branches in any amount. If one gathers wood to improve the tree, he is liable in any amount; for use as fuel, he is liable for collecting enough to cook a chicken egg. If one gathers herbs in order to improve the bed of earth, he is liable in any amount; for use as animal fodder, he is liable for collecting enough to fill a kid's mouth.

Shabbos 12:3

One is liable for writing two letters, with either hand, whether two different letters or the same letter twice, even from two different inks, and in any language. Rabbi Yosi says that two letters is the standard because that's what they did with the boards of the Mishkan (Tabernacle): they would write letters on the boards so they would know which were meant to go adjacent to one another. Rebbi says that one is liable for writing a small name that's part of a longer name that one had intended to write. Examples include "Shem" from Shimon or Shmuel, "Noach" from Nachor, "Dan" from Daniel, and "Gad" from Gadiel.