Questions & Answers about Подойди к столу и возьми карандаш.
подойди is the perfective imperative of подойти (“to approach”). It tells someone to perform the action once and bring it to completion: “go up/come over.”
подходи is the imperfective imperative of подходить, suggesting a repeated or ongoing action (“keep coming over” or “approach habitually”). In this instruction you want the learner to approach the table one time, so the perfective подойди is appropriate.