用 may have pictured a bucket or a bell — a useful tool you pick up and employ. It was borrowed long ago for the abstract verb 'to use', and that's its everyday job now.
用 is 'to use': 用心 (with one's heart = attentively/diligently, with 心), 用手 (use your hands, with 手). It also forms 有用 (useful, 'have use', with 有) and its opposite 没用 (useless). The most useful 用 of all for a beginner is 不用 (bú yòng) — 'no need / don't bother': 不用谢 ('no need to thank' = 'you're welcome', pairing with 谢!), 不用了 ('no thanks, I'm good'). A small character that politely waves things off.
A handy tool you pick up — to USE.
不用谢 ('no need to thank') is a common 'you're welcome' — and it reuses 谢 from week one. 用心 ('use heart') means to do something attentively, with care.