Stop after a brief taste; dabble without going deep.
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辄 is classical/literary. Modern Chinese uses 就 (jiù) for 'then, immediately'. You'll meet 辄 mostly in chengyu like 动辄 (at every turn) and 浅尝辄止 (to dabble), or in classical texts. Don't use it in conversation.
history
Originally 辄 named the upturned end-boards of a chariot box that resembled drooping ears. By the Han dynasty it had been borrowed for the adverbial 'then, immediately', preserved today only in fixed expressions.
