to commit to memory; to keep in mind; to memorize or internalize information.
試験に出る単語はしっかり頭に入れておこう。
Make sure to memorize the vocabulary that will appear on the exam.
先生のアドバイスを頭に入れて、次は気をつけます。
I'll keep the teacher's advice in mind and be careful next time.
手順を頭に入れてから作業を始めてください。
Please commit the procedure to memory before you start the work.