groundwork; solidifying the fundamentals; training of the basics
Refers to the process of establishing a firm foundation, often in learning, sports, or projects.
When learning a new language, solidifying the fundamentals is important.
As groundwork before the season, I run every day.
土台作り also means building a foundation, but often has a more concrete or structural nuance, while 基礎固め is commonly used for abstract skills or knowledge.
Compound of 基礎 (foundation) and 固め (hardening, strengthening), from the verb 固める (to harden, to solidify).